A study addressing commercial beneficial insect habitats found some seed mixes had variable species composition, reduced germination, and when planted according to supplier recommendations were eliminated by weed competition. A small proportion of insects attracted to habitat plants were natural enemies useful in crop insect management. A number of plant feeding insects were harbored by habitat, and night-flying pest moths were fed by some habitats. A commercial habitat planted around organic tomatoes did not affect parasitism, predation, or pest insect numbers. Habitat plantings did attract parasitic insects, but the flowers themselves did not appear to be responsible for this attraction.
1. To evaluate commercially available beneficial insect seed mixtures for purity, composition, and germination rates.
2. To monitor the communities of insects, both beneficial and otherwise, attracted to commonly planted cut flowers and cover crops on organic farms
3. Based on currently available literature, construct and evaluate a simple beneficial insect habitat designed to attract and build populations of Trichogramma wasps and Cotesia congregata, well-known parasitoids of eggs and larvae, respectively, of tomato fruitworms and hornworms.
Background of Problem.
Producers of organic crops have many insect pest species they must manage. In some cases, insect pests are so overwhelming that growers either accept damage or completely abandon the crop. Organic grower’s concern about this situation is reflected in a cooperative survey administered by Carolina Farm Stewardship Association and N. C. State University. In 2000, N.G. Creamer and T. Kleese (unpublished data) conducted a survey of North and South Carolina organic growers asking them to list their most important research needs. Results indicated the number one response was “insect pests”. When growers were asked to prioritize research needs for resolving insect pest problems, beneficial insects and beneficial insect habitat were their first and second choices.
Clearly growers are focusing attention on habitat manipulation as a way to help manage pest insects. However, there is little research-based, objective, information available to provide advice on how to construct or maintain this habitat. Commercial interests have filled this void by providing pre-mixes of plants advertised as attracting beneficial insects. To many growers this seems like a convenient way to establish habitat. There may be problems with this approach. These mixes may not germinate under conditions found in the southeast. Poor germination by one or more species may fail to provide a needed resource and compromise the whole planting. Even after germination the perennial species may not be adapted to the southeast, requiring replanting. Additionally, there is no guarantee that what is advertised is in the bag.
Most organic farms depend on cut flowers for additional income. In some cases flowers can represent one-half or more of growers total income. So a mix of flowering species and cultivars are a substantive part of organic farm landscapes. Since this is likely to be a permanent part of organic farms (especially for small and limited resource farms) it seems prudent to examine the role of these plantings on beneficial insects. Flowers may enhance or antagonize other habitat intended to attract beneficial insects. Perhaps extensive flower plantings preclude the need for additional habitat for beneficial insects.
Habitat requirements for beneficial insects overlap with the resource needs of certain pest species. For example, some Lepidoptera pest species benefit from a readily available source of nectar. They may lay more eggs over their lifetime and the eggs are more viable. So habitat planted with the intent of attracting beneficial insects will also attract pest species and may exacerbate pest problems locally. So it becomes important to determine if the habitat provides a net gain by beneficial insects destroying more pest species than are attracted to the habitat. This complex interaction cannot be unraveled easily. However, like all difficult problems, investigations need to be put in the field that methodically examine this problem. No one experiment will completely answer all questions but a first step is needed to start the process.
The authors began research on beneficial insects influence on pest populations on organic farms in 1994. A SARE funded study (AS94-013 “Assessing the Impact of Beneficial Insect Populations on Organic Farms”, G. G. Kennedy, H. M. Linker, D. B. Orr) gave us the opportunity to directly measure the effect of a common parasitoid (Trichogramma) on caterpillar pests on small, organic farms. Additionally, we evaluated the quality of commercially produced Trichogramma that were being purchased by some of the growers. We found that natural Trichogramma populations were so high that purchasing them was unnecessary (Schmidt 1998) and that the quality of purchased Trichogramma was disappointing (Schmidt et al 2003). The result of this project was that we were able to give growers direct advice on purchased inputs. We are confident that we will be able to do the same at the conclusion of the proposed project. This project also gave the authors an opportunity to determine the suitability of organic farms for beneficial insect habitat research. There are many advantages and some limitations to research on organic farms. For the project proposed herein, we determined that the ability to control surrounding habitat and crops was not possible on farms thus we intend to conduct this research on the certified organic unit at the Center for Environmental Farming Systems.
Growers on organic farms need some guidance as soon as it can be provided. This proposed study seeks to provide data that will give growers advice on the methods that are currently being implemented to try to enhance natural enemy populations.
Manipulating vegetative habitat on organic farms in order to increase resident natural enemy populations is a popular idea. Over the last 10 years, academic research has been directed toward increasing beneficial organisms by manipulating vegetation both within and surrounding crop fields (for a summary of this work see Barbosa 1998 and Pickett and Bugg 1998). This type of research has proved to be very complex and has been directed primarily at understanding the underlying ecological mechanisms. The slow pace of data collection (due to the complexity of the problem) has resulted in virtually no research information to make recommendations on how to design farms and specific natural enemy habitats to enhance insect pest management. Much basic research remains to be done before researchers can commonly make specific recommendations to growers on how to build and maintain these habitats (Wratten et al. 1998).
It is a strongly held belief that diversification of plants in and around commercial crops will improve biological control of pest species, and this belief is supported by research (Landis et al. 2000). The foundation of this approach is that a more complex agroecosystem will mimic the natural system that existed before agricultural disturbances. What is inferred is that more beneficial insects are attracted to a diverse landscape resulting in more pest insects being destroyed. However, diversification can have both negative and positive results. Non-crop vegetation and intercrops may compete or otherwise interfere with economic crops, and this same vegetation may support key pests or serve as a source of plant pathogens (Pickett and Bugg 1998).
There are several general characteristics that should be included in beneficial insect habitat. These include over wintering sites, increased quantities of pollen and/or nectar, a source of alternate prey, and food resources for predators that occasionally feed on plants (Sloggett and Majerus 2000; Sunderland and Samu 2000; Carmona and Landis 1999). Specific combinations of plants that will provide this benefit are not clear from research data, and in fact, there is a notable gap between research and implementation of this type of biological control (Ehler 1998). Any area maintained for beneficial habitat must result in a net gain in beneficial insects and net reduction in pest insects but it is difficult to determine this (Landis et al. 2000). In addition, if habitat areas are too attractive to beneficial insects they will not move into surrounding cropland (Carmona and Landis 1999).
Organic growers have long practiced culturing specific plants and plant groupings to attract beneficial insects (and repel pest species). However, these growers have little guidance from research institutions, so they are using many different approaches in an attempt to improve natural control. For example, undisturbed habitat may be left around production fields allowing natural vegetation to flourish. Weeds can provide essential resources for beneficial insects (Samu et al. 1999; Banks 1999; Altieri and Paoletti 1999). However without management these areas will reach successional stages that may not have the plant composition needed to support beneficial insects. Thus management of these areas becomes problematic. Succession can be stopped or delayed by selective herbicides but this option is not available to organic growers. Mechanical maintenance may be possible but little information is available to guide decisions. Additionally, permanent habitat may not provide the benefit sought. Certain important insects may not be able to emigrate far outside the permanent boundaries. For example, ground beetles are critical insect predators and consume weed seeds (Menalled et al 1999). However, they must walk from over wintering habitat to re-invade crop fields. It may be weeks or months before they completely colonize new plantings (Landis et al. 2000). The larger the field the slower the process. So permanent (managed or unmanaged) field borders may contribute to natural control of insects but clearly will not provide all needed resources.
Intercropping also provides an opportunity to provide habitat for beneficial insects (Sunderland and Samu 2000) but this method of crop production is seldom practiced in the US. Serial plantings (or relay plantings) may be effective habitat as insects are forced from a senescing resource to crop plants (Parajulee and Slosser 1999; Bottenberg et al 1997; Bugg et al 1991). Growing living mulches or intercropping commercial crops may also be useful but due to logistical complexities and yield penalties this approach has not been popular. Additionally, results to date have shown mixed efficacy at controlling target pest insects. (Hooks et al 1998; Platt et al 1999; Banks 1999; Carmona and Landis 1999). No matter which approach is used, careful consideration must be given to plant selection to avoid providing resources to pest species. For example, in a research trial conducted in the Fall, 2003 in North Carolina, a buckwheat-German millet mixture intercropped with cabbage increased the number of pest insects relative to non-intercropped cabbage resulting in more plant damage (L. Jackson 2003 unpublished data).
For Objective 1:
Commercial Sources. Three commercial seed mixes were purchased in January 2003, and three seed mixes were purchased in September 2004. Due to seed cost, packaging and availability, in 2004 the seed mix from Company 4 was used instead of Company three’s mix. Both mixes were deemed to have the same species present, with the addition of Globe Gilia in the Company 4 mix.
Each of the three packages from Company 1 arrived in 170 g cylindrical cardboard canisters (20.4 by 7.8 cm) with one metal and one plastic endcap. The three packages from Company 3 contained 28.4 g of seed mixture sold in paper envelopes (12.4 cm by 10.1 cm) and Companies 2 and 4 were packaged in brown-paper bags secured with packing tape and contained approximately 2.3 kg of the seed mixture.
Seed Separation and Identification. In 2003, three entire canisters from Company 1, three envelopes from Company 3 and one 2.27 kg bag from Company 2 were separated into individual seed components. In 2004, each container of purchased seed were thoroughly mixed using a riffle-type sample splitter (Humboldt Manufacturing Co., 7300 W. Agatite Ave, Norridge, IL 60706-4704) and one-55 g subsample was removed from three separate canisters from Company 1, and three-55 g subsamples were removed from packages fromCompanies 2 and 4.
Seed species were separated from each other using an air column seed separator (South Dakota Seed Blower (model 757), Seedburo Equipment Co., 1022 West Jackson Boulevard, Chicago, IL 60607), various sized sieves (300-600 micrometer) (Hoffman Manufacturing, Inc., P.O. Box 547, Albany, OR 97321) and hand separation using a camel hair paint brush and fine tipped forceps. Each component was weighed separately and the percentage of each species calculated by weight and by relative numerical abundance. Samples from all companies were sent to the North Carolina Department of Agriculture & Consumer Services, Plant Industry Division – Seed Section for identification.
Germination. In 2003, germination tests were conducted on 100 randomly selected seeds of each species from each of three containers from Companies 1 and 3 and two subsamples from Company 2. In 2004, 100 randomly selected seeds from each of three-55 g subsamples from Companies 1, 2 and 4. If less than 100 seeds of a species were present in a subsample, all seeds were subjected to germination tests. For seeds less than 5 mm in length, two pieces of germination blotter paper (Steel Blue Germination Blotter Paper, Anchor Paper Company, 480 Broadway, St. Paul, MN 55165-0648) were placed in the bottom of sterile 100 by 15 mm polystyrene petri dishes (Fisher Scientific, P.O. Box 4829, Norcross, GA 30091) using either a Gast Vacuum Seed Planting System (Hoffman Manufacturing, Inc., 16541 Green Bridge Rd., Jefferson, OR 97352-9201) or hand placement and moistened with 10 ml of distilled water. Seeds greater than 5 mm in length were placed in hinged acrylic boxes (18.5 by 13.5 by 5.0 cm) with two pieces of germination blotter paper covering the bottom and moistened with 60 ml of distilled water. Excess water was drained off prior to seed placement.
Up to six petri dishes were labeled and randomly placed on plastic trays (30 by 41 cm). Each tray or hinged acrylic box was enclosed in a plastic bag (25.4 by 61.0 cm) to prevent excess water loss and placed into a controlled environmental chamber (SG8 Germinators: Hoffman Manufacturing Inc., P.O. Box 547, Albany, OR, 97321). Germinators were set at 15oC, 20oC or 20/30oC (with 16-hours at 20oC) and a 12-hour photoperiod. Germination testing procedures for each species followed recommendations in the Association of Official Seed Analysts – Rules for Seed Testing (2002).
Seeds were considered germinated if the radicle was twice the length of the seed. Seeds recorded as germinated, were removed from dishes. Seeds that failed to germinate and could not be classified as dead were subjected to a Tetrazolium Chloride Test (TZ), whereby seeds were placed in a 1.0% solution of 2, 3, 5-triphenyl-tetrazolium-chloride (Grabe 1970) and soaked for 24-hours at 30oC to determine viability.
Data Analysis. Seed data were recorded using the following parameters.
Percentage of seeds by weight = (Weight of individual seed species/ Total weight of seed for one container) x 100. Average weight of one seed of each species = Sub-sample weight of 50 seeds/ 50. Percentage of seeds based on numerical abundance = [(Total weight of each seed species/ Average weight of one species seed)/ Total number of seeds in the container)] x 100. Percent germination = (Number of germinated seeds/ Total number of seeds tested) x 100.
For Objective 2:
Seed Sources. All seeds were purchased in February 2003. The three commercial habitat sources were: Border Patrol™ (Clyde Robin’s Seed Company, P.O. Box 2366, Castro Valley, CA 94546-0366), Beneficial Insect Mix (Heirloom Seeds, P. O. Box 245, W. Elizabeth, PA 15088-0245), Good Bug Blend (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945). The cut flower/ herb seed sources were: Foeniculum vulgare var. bronze fennel (Family: Apiaceae), Zinnia elegans var. pastel dreams (Family: Asteraceae) and Celosia cristata var. cockscomb amaranth (Family: Amaranthaceae). Seed composition of each of the commercial blends is presented in Table 1.
Plants. For each of the commercial habitat mixes, seeds were separated from one another using an air column seed separator (model 757, South Dakota Seed Blower, Seedburo Equipment Co., 1022 West Jackson Boulevard, Chicago, IL 60607), various sized sieves (Precision Eforming LLC, 839 Rte. 13, Cortland, NY 13045), and hand separation (Forehand 2005). The relative numerical abundance of each seed species was estimated for planting in the greenhouse and transplanting into the field. Transplants were started late March in greenhouses at North Carolina State University and each species was planted separately, with the exception of the clover and alfalfa from Good Bug Blend, which were planted in a mixture. When plants reached 10cm tall, they were transplanted into field plots.
Experimental Design. This study was conducted in 2003 at the Center for Environmental Farming Systems (CEFS), Goldsboro, NC. All plot areas and surrounding crop fields were pesticide free for at least three years prior to this study and were transitioning towards organic certification.
In order to maximize distance between flowering habitats, this study was set up using a complete block design with selective placement of treatments. Three blocks were planted with the same order of treatment plots as follows: Celosia, fennel, Border Patrol™, Good Bug Blend, Zinnia and Beneficial Insect Mix. The first block bordered various solanaceous crops; the second block was 58.4m to the south, bordering a mix of brassica crops; and the third was 38m to the southeast and planted beside corn and clovers. Plots within each block were surrounded and separated by a 1.5m buffer that was planted with brown-top millet (Wyatt Quarles, P.O. Box 739, Garner, NC 27529) and mulched. Each plot with Celosia, fennel or Zinnia was 6.1 X 2.1m, planted in three rows 76cm apart, with 30.5cm between each transplant. While there was likely to be some movement of insects between plots, this study was conducted to estimate the relative attractiveness of each habitat to insects, and the insect communities harbored by each. Therefore, insect movement should not have affected our relative results.
Transplanting design for the commercial habitat seed mixes was based on the numerical abundance of each species present in each mix (see Forehand 2005). Plywood templates with a pair of 10.2cm holes cut every 0.09m2 was used as a guide to ensure uniformly spaced plants (Forehand 2005). For Border Patrol™, a 1.5 X 0.6m template was used 12 times per plot; four times lengthwise and three times across, so that each plot measured 6.0 X 1.8m. Transplanting locations for angelica and strawflower were left empty as seeds did not germinate. For Beneficial Insect Mix, a 1.5 X 0.9m template was used 8 times per plot, four times lengthwise and two times across so each plot measured 6.0 X 1.8m. The planting template for Good Bug Blend employed a 1.2 X 3.0m template to accommodate the high variability in abundance of the 14 plant species (Forehand 2005). The template was used 2.5 times and plots measured 6.0 x 1.2m.
Plot Management. In April of 2003, soybean meal (Wyatt Quarles, P.O. Box 739, Garner, NC 27529) which had not been treated with pesticides was applied to each plot at a rate of 78.5kg/ha and incorporated with rakes. All plants were transplanted 15-18 May 2003 utilizing the templates as a guide and hand trowels and bulb diggers for planting. All plots were then mulched with organic wheat straw. For two weeks following transplanting, any dead plants were replaced. Plants were watered as needed and weed management consisted of hand-weeding within plot and mechanical control around and between plots.
Foliar and Floral Sampling. On eight dates in 2003 (19 June, 25 June, 3 July, 9 July, 16 July, 23 July, 30 July, 6 August), insect samples were collected from each plot using a D-Vac (D-Vac, Inc., 3891 N. Ventura Ave., Ventura, CA 93001) vacuum sampler for one minute per plot and two 30.5cm aerial nets (Bioquip, 321 Gladwick Street Rancho, Dominguez, CA 90220) for one minute prior to and during sampling with D-vac. Sampling was conducted between 11:00 and 14:00 hours, when insect numbers were expected to be greatest (Jervis and Kidd 1996). Samples were collected from one of the outside rows of Celosia, fennel and Zinnia and down one side of the three habitat mixes. In order to allow insect communities and plants to recover, the sides of plots sampled each week was alternated so that no side was sampled more often than every two weeks. Family level identification was performed on all insects larger than 3mm. For insects less than 3mm, identifications were done for specimens from three 5.5% subsamples from each plot. Numbers from the combined subsamples were scaled up to provide a single estimate of the number of smaller specimens from each family in each plot.
Moth Sampling. Observations of flower visits by adult Lepidoptera were made on four dates in 2003: 24 July, 30 July, 6 August, and 13 August. Observations began at dusk (approximately 18:30 hours) and continued until total darkness, approximately 1h later. Each plot was observed three times during the hour for 1min using flashlights covered with red cellophane. The red light produced allowed us to take advantage of insects general lack of sensitivity of longer light wavelengths (Atkins 1978), so we could clearly see the moths, but not attract them to our light source. The total number of noctuid moths (Lepidoptera: Noctuidae) and hawk moths (Lepidoptera: Sphingidae) visiting each plot was recorded. Samples of these moths collected. The noctuids included both tobacco budworm, (Heliothis virescens (F.)), and tomato fruitworm, Helicoverpa zea (Boddie). Sphingids were primarily tobacco hornworm, Manduca sexta L., with some white-lined sphinx moths, Hyles lineata (F.). All of these species are considered pests of crop plants grown on the CEFS Farm. If a moth moved between plants in the same plot without leaving the plot, it was counted only one time. If a moth left the plot then returned, it was counted as a second visit. Moths were collected on 24 July using aerial nets for identification.
Pitfall Traps. In order to sample ground beetles (Coleoptera: Carabidae) and spiders (Araneae), one pitfall trap was placed into each of the three plots for each of the different plant communities on seven dates in 2003: 26 June, 10 July, 17 July, 25 July, 31 July, 7 August and 14 August. Pitfall traps were constructed using two-473 ml plastic cups (Solo Cup Company, 1700 Old Deerfield Road, Highland Park, IL 60035) set inside of each other. The outer cup had drainage holes cut in the bottom while the inner cup had holes on the sides, approximately 6cm from the top. Pitfall traps were randomly placed in the ground so that the upper lip of the cup was even with the soil surface and filled with approximately 2.5cm of 50% antifreeze (Honeywell International Inc., 101 Columbia Rd., Morristown, NJ 07962). Traps were set at approximately 10:00 hours and samples were collected 24h later.
Insect Identification. Insects were identified using the following sources: Bland and Jaques 1978, Borror et al. 1989, Borrer and White 1970, Flint and Dreistadt 1998, Gibson et al. 1997, Grissell and Schauff 1990, McAlpine et al. 1981, 1987, Mitchell 1960a, 1960b, Mullen and Durden 2002, Stehr 1987, 1991, White 1983. Following identification, insects were grouped into feeding groups (Table 2) based on consensus information obtained from Borror et al. (1989), Borror and White (1970) and Flint and Dreistadt (1989). The “parasitoid – mixed” feeding group consisted of families with very diverse life histories and which could not be overall categorized as beneficial or detrimental. The “parasitoid – non-crop” feeding group consisted of families that were less likely to contribute to the suppression of important agricultural crop pests (eg. Scoliidae and Tiphiidae are scarab beetle larval parasitoids). “Inconsequential predators” were categorized because of their varied life histories. For example, Cucujidae and Lampyridae seldom occur in numbers that would impact pest populations, while Sphecidae usually feed on a single type of insect or spider.
Reference collections were assembled and later verified by one of the following: David Stephan, Robert Blinn, Dr. Brian Wiegmann of North Carolina State University or Dr. Ken Ahlstrom, North Carolina Department of Agriculture and Consumer Services – Plant Protection Section.
Data Analysis. For each feeding group, six diversity indices were calculated: Simpson’s Index; Shannon-Wiener’s Index (often called Shannon’s Index); Hill’s N1 and N2 diversity numbers; species evenness [exp(Shannon)/species richness]; and species richness (Hill 1973). Because the diversity index literature does not present a clear favorite index, and because different indices perform better under varying circumstances, we chose to calculate and present these six commonly used indices (Mouillot and Leprêtre 1999, Peet 1974, Hill 1973). Diversity measures were analyzed using a split plot ANOVA with habitat as a whole plot factor and date as a subplot factor, with whole plots in blocks (PROC GLM, SAS Institute 2002). Habitat was tested against block*habitat (with 10 denominator df) and date and habitat*date were tested against sub plot error (with 79 denominator df). Means were separated using LS means (SAS Institute 2002).
For Objective 2:
Research site. Research was conducted at the Center for Environmental Farming Systems Small Farms Unit near Goldsboro, N.C. The Small Farm Unit is a highly diverse, organic farm approximately 6.07 ha in size. A wide variety of commodities are grown at the Small Farm Unit including vegetable, grain, flower, forage, small fruit crops, and some livestock production.
Experimental design Two experiments were conducted for this study. In experiment 1, observational data were collected from three 56.4 x 2.7 m flower strips separated by an average distance of 48.2 m. In 2004, each flower strip had five 6.1 x 2.7 m plots laid out using a complete block design with a predetermined placement of plots (i.e. the order of plots was the same in all three flower strip replications due to constraints imposed by the Small Farm Unit’s management system). Three had commercial beneficial insect habitat seed mix plantings; one had fennel, and one had buckwheat (Table 1). See Forehand (2004) for plot details. In 2005, flower strips had six 6.1 x 2.7 m plots laid out using a complete block design with a predetermined placement of plots. Plots were laid out in the following order from the northeast to the southwest: cock’s comb (Celosia cristata L. ‘Cramer’s Crested Burgundy’), fennel (Foeniculum vulgare P. Mill. ‘Smokey Bronze’), yarrow (Achillea millefolium L. ‘Silver Queen’), black-eyed Susan (Rudbeckia hirta L. ‘Indian Summer’), buckwheat, and Shasta daisy (Leucanthemum x superbum (J.W. Ingram) Berg. ex Kent. ‘Alaska’).
In experiment 2, measurements of the abundance of microhymenoptera in habitat plantings were collected from three flower strips measuring 56.4 x 2.7 m separated by an average distance of 48.2 m. Each flower strip had seven 6.1 x 2.7 m plots laid out using a complete block design with predetermined placement of plots. Plots were identical to 2005 observational plots with an additional plot at the southwest end of each replicate dominated by naturally occurring crabgrass (Digitaria spp. Haller) that served as a control.
All flower heads were removed from half of each treatment plot using pruning shears and half of each control plot was mowed on 29 July, 2005. A coin toss was used to determine from which side of the plot to remove flowers. Flower removal prior to bud-break and mowing occurred for the remainder of the study.
Plot management. In 2004 and 2005, plants were watered as needed and weeds were controlled by hand inside plots and mechanically mowed around plots. In 2005, plots containing previously established fennel and yarrow were utilized because sufficient plant densities were present. All other plants were either transplanted or directly seeded into plots on 25 May, 2005.
Cock’s comb, black-eyed Susan, and daisy transplants were grown in the Biological Control Greenhouse at North Carolina State University, Raleigh, NC. Heating set point of the greenhouse was 21.1º C and ventilation set point of 26.7º C. Plants were started in 96-cell round plug trays (3.8 by 3.9 cm, Hummert International, 4500 Earth City Expressway, Earth City, MO) filled with moistened Metro-Mix 200 potting soil (Scotts-Sierra Horticulture Products Co., The Scotts Company, 1411 ScottsLawn Rd., Marysville, OH) on 25 and 28 March, 2005. Plants were watered as need with a misting bed and/or hand watering. Trays were placed under high intensity metal halide lights with an 11 h photophase that was extended to 16 h on 22 April, 2005. When roots were established and the aboveground portion was of sufficient size, plants were transplanted to 473 ml plastic cups (Kmart Corporation, Troy, MI) with a drainage hole drilled in the bottom using a 1.3 cm drill bit. Prior to transplanting, plots were tilled and all plot borders as well as cock’s comb, black-eyed Susan, and daisy plots were covered with woven black plastic ground cover (Wyatt-Quarles Seed Company, 730 Hwy 70 West, Garner, NC) secured with landscape anchor pins (DuPont™ Garden Products™, Chestnut Run Plaza, Bldg. 728, PO Box 80728, Wilmington, DE) to suppress weeds and preserve soil moisture.
Fifty-four plants of each species were planted per plot in three rows with 30.5 cm between each plant and 46 cm between each row using hand trowels and bulb diggers. Buckwheat was directly seeded into plots at a rate of 56 kg/ha and raked in using a steel rake. Buckwheat seed was purchased from Jeffrey’s Seed Co. (1608 US 117 South, Goldsboro, NC). The remaining seeds were purchased from Germania (5978 N Northwest Hwy, PO Box 31787, Chicago, IL).
Sampling. In both years of experiment 1, one observation of insect flower-feeding per plant species was made in each replicate on each sampling date. Observations of insect feeding were conducted on seven dates in 2004 (2 June, 9 June, 24 June, 8 July, 14 July, 22 July, and 4 August) and on thirteen dates in 2005 (21 June, 24 June, 28 June, 1 July, 5 July, 12 July, 15 July, 18 July, 2 August, 5 August, 9 August, 12 August, and 16 August). Observations in 2004 began between 12 and 1 pm. This time was chosen after performing a daylong observation of insect activity on 31 May, 2004, from dawn to dusk where we found the greatest amount of activity to occur midday. Observations were made at 9:30 am and 12:00 pm in 2005. The 9:30 observation was added due to low average numbers of insects found feeding midday on buckwheat in 2004, presumably because peak nectar production in buckwheat occurs in the morning (Olson et al. 2005; Free 1993).
A single observer called out identified insects to a recorder who also kept time. This approach allowed the observer to watch flowers for the prescribed period without interruption. For a single observation, the observer constantly scanned an approximately 0.3 m2 area of actively blooming flowers of a single plant species for two minutes. Insects observed directly feeding from flower heads were recorded to family level. Feeding was considered to be direct application of the insects’ mouthparts to the area of the plant producing nectar and/or pollen or apparent application of the mouthparts to this region accompanied by movement of the head or body into the floral structures. Insects that moved from flower to flower within the area of observation were counted once. Insects that left the area and returned were counted a second time, similar to methods described by Colley and Luna (2000).
All insects that were too small to be identified in the field were removed with an aspirator and transferred to a vial containing 50% ethanol and returned to the laboratory for identification. Preliminary identifications were confirmed by David Stephan, North Carolina State University. Specimens were placed in the NCSU Insect Museum as vouchers.
In experiment 2, sticky traps were used to monitor microhymenoptera. Traps were made from 51 mm sections of 19 mm diameter PVC pipe spray painted with yellow plastic enamel (The Valspar Corporation, Wheeling, IL) and wrapped with tanglefoot-coated clear acrylic sheets (Great Lakes IPM, 10220 Church Rd. NE, Vestaburg, MI). In each plot, traps were placed on a single stake at three heights: 0.5 the height of flowers, flower height, and 1.5 times flower height. Traps were secured to plastic stakes with a clothes pin and were changed twice weekly from 9 August to 16 August, 2005.
Immediately following collection, traps were returned to the laboratory where tanglefoot-coated acrylic sheets were removed from PVC sections, sandwiched between two sheets of clear plastic wrap (Kmart Corporation, Troy, MI), and placed in plastic freezer bags (1 qt., Hefty®, Pactiv Corp., 1900 W Field Ct., PO Box 5032, Lake Forest, IL) for storage in a freezer at -20º C. Using a dissecting microscope (Leica, Wild MZ8, Leica Microsystems GmbH, Ernst-Leitz-Strasse 17-37,Wetzlar) the number of individuals in the families Mymaridae, Scelionidae, and Trichogrammatidae on each sheet was recorded.
Data analysis. For experiment 1, insects observed feeding on flowers were grouped according to six feeding guilds: crop parasitoids, non-crop parasitoids, deleterious parasitoids, crop predators, deleterious predators, and pollinators. Members of the families Figitidae, Eulophidae, and Tachinidae were considered crop parasitoids; Scoliidae and Tephiidae non-crop parasitoids; Chrysididae deleterious parasitoids; Anthocoridae, Cantharidae, Coccinellidae, Chyrsopidae, Lygaeidae, Sphecidae, Staphylinidae, and Vespidae crop predators; Pompilidae deleterious predators; and Anthophoridae, Apidae, Halictidae, and Megachilidae pollinators.
Experiment 1 feeding insect counts were square root transformed to normalize the data then analyzed using a general linear model and mixed models for each feeding guild (PROC GLM, PROC MIXED, SAS Institute 2003). Plant species that flowered in only one replicate or received no feeding visits from members of a specific feeding guild were omitted prior to analyses to avoid skewing results. Dates of observations that fell within the same week in 2005 were combined prior to analyses to reduce imbalance in data due to differences in blooming period among plant species. Experiment 2 abundance data were square root transformed then analyzed using general linear models (PROC GLM) and least significant.
For Objective 3:
Experimental Design. This study was conducted in 2003 and 2004 at the Center for Environmental Farming Systems (CEFS), Goldsboro, NC. Plots were located in areas of CEFS that were pesticide free for at least three years before this study and were transitioning to organic certification. The study was set up using a randomized block design with selective placement of treatments, and six replications. Rather than being side-by-side, treatment and control plots were separated by 45-61 m, to reduce the likelihood of beneficial insects moving between treatment and control plots. Two pairs of plots were located on the agriculturally diverse Small-Farms Unit. An additional two pairs of plots were located on the organic unit, approximately 0.8 km to the east in fields bordered on one side by mature hardwood trees near fields containing cotton, wheat and sweet potatoes. The final two pairs of plots were located on the organic unit approximately 2 km southwest from the Small-Farms Unit and were surrounded by large-scale commodity fields. All plots were in the same location both years of the study, with the exception of one control plot in the field bordered by hardwoods, which was moved 15.8 m further from its paired treatment plot due to excessive tomato disease pressure.
Each plot (8.2 by 15.8 m) contained four 13.7 m rows of tomato (Lycopersicon esculentum Mill. var ‘Amelia’(Clifton Seed Co., P.O. Box 206, Dobson, NC 28341)) plants transplanted 0.9 m apart on 1.5 m row spacing. Treatment plots were surrounded by a transplanted 0.6 m border of beneficial insect habitat, while control plots were surrounded by a border of direct-seeded brown-top millet (Brachiaria ramose (L.) Stapf.). Millet in control plots was maintained below 2 ft in height as a forage crop so that no seed heads were formed, and no seed head feeding insects were attracted to the crop. Millet was chosen for control borders because of the low abundance of insect herbivores in North Carolina and the lack of floral resources. A literature search revealed no publications addressing frequency and severity of forage insects on millet in North
Carolina. The millet borders simulated grassy field borders, which are the most common type of border on organic farms in this area.
Crop Management. Before transplanting in 2003, all plots were tilled and plots fertilized with untreated soybean meal (1,547 kg/ha, J. Milo Pierce Farm Center, Inc., 3626 Nahunta Road, Pikesville, NC 27863) and Solubor (7.6 kg/ha, Borax, Inc. 26877 Tourney Road, Valencia, CA 91355-1847). Soaker hoses (Aquapore Moisture Systems, Inc., A Fiskars Co., 610 S. 80th Ave., Phoenix AZ 85043) were placed along the center of each row and each plot mulched with 10-15 cm of pesticide-free wheat straw. Tomatoes were transplanted on 14-16 May, 2003 and supported with sisal twine (The Lehigh Group, Macungie, PA 18062) secured to wooden stakes (0.02 by 0.02 by 1.4 m) with a 2.7 m stake spacing. Plants were irrigated as needed and all plots had at least a 1.2 m buffer area surrounding all sides, which was planted with brown-top millet and kept mowed to aid in weed suppression.
Tomato plants, stakes and soaker hoses were removed from each plot in September 2003 and each plot was tilled (tiller model 852, BCS America, 8111 NE Columbia Blvd, Portland, OR 97218) and crimson clover seed (Trifolium incarnatum L.) (variety ‘Au Robin’, Wyatt Quarles, P.O. Box 739, Garner, NC 27529), inoculated with Rhizobium (Urbana Laboratories, 2202 Locust St, St. Joseph, MO 64501) was raked in at a rate of 1,547 kg/ha. In treatment plots, the area inside and outside of the habitat border was seeded with crimson clover, whereas control plots had the entire area seeded.
In April 2004, untreated soybean meal was applied to each plot at a rate of 1,547 kg/ha and incorporated with the clover residue using a hand tiller. Before tomato transplanting, soaker hoses were placed down the center of each tomato row and each row covered with 1.22 m polyester landscape fabric (Easy Garden Products, Ltd., 3022 Franklin Avenue, Waco, Texas 76710) for weed suppression. Tomato plants were transplanted (May 18-20, 2004) through holes cut in the landscape fabric. Plants were supported with nylon twine (The Lehigh Group, Macungie, PA 18062), staked, and hand watered as needed throughout the growing season. All plots had at least a 1.2 m buffer area surrounding all sides, which was planted with brown-top millet and kept mowed to aid in weed suppression.
Habitat Management. A 0.453 kg package of Good Bug Blend (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945) was obtained anonymously in January 2003. Seeds were separated by species and the relative numerical abundance of each seed species calculated. Due to the low success of this seed mixture when direct seeded (unpublished data, M. Kroner, North Carolina State University, Raleigh, N.C), it was decided transplants would offer the greatest possibility for success.
Transplants of each seed species were started in a greenhouse and plants were transplanted into the field 14-16 May 2003,and watered as needed. Transplanting design for the habitat border reflected the numerical abundance of each species present in the Good Bug Blend seed mix (see Table 1 and Forehand 2005). Throughout the summer of 2003, the habitat area was hand weeded. Habitat was allowed to over-winter and reseed and no hand weeding was conducted within the habitat plantings in 2004.
Millet borders around control plots were planted 14-16 May 2003 both years of the study. These borders were mowed to approximately 15 cm during both growing seasons.
Sampling – Egg Fate. The influence of habitat on H. zea egg mortality was assessed by caging moths on tomato plants and monitoring the fate of their eggs. On six dates in 2003 (16 July, 23 July, 30 July, 6 August, 14 August, 19 August), five plants per plot were randomly selected and one leaf on the upper third of the plant was used for caging gravid moths (obtained from the North Carolina State University (NCSU) Insectary). A cheesecloth bag (22 by 43 cm) with three to six moths was secured overnight on the selected leaf. Five eggs were randomly selected on each leaf and all other eggs removed. Detailed maps of egg locations on each leaf were recorded on paper tags (12 by 6 cm, Avery-Dennison, Brea, CA 92821) and secured to the base of each leaf using wire. Eggs were left in the field for one week, after which the fate of each egg was recorded based on work by Suh (1999).
Due to erratic egg production by insectary-raised moths the first year of the study, eggs from field populations of H. zea and Manduca spp. as well as insectary-reared Manduca sexta L. were evaluated on three dates in 2004 (27 July, 2 August, 10 August). For field populations, plants were scouted and where possible, twenty-five freshly oviposited eggs were evaluated per plot (see Suh 1999). Eggs were located and a detailed map of the location of each egg on each leaf was drawn on a paper tag (4.3 by 7.0 cm, Avery-Dennison, Brea, CA 92821), secured to the base of the leaf using string. After two days, these leaves were removed from plants, inserted into water pics (Syndicate Sales, 2025 N. Wabash Street, Kokomo, IN 46901), placed in sealed 3.8 liter plastic bags and held in the laboratory at room temperature near a window with indirect sunlight. Seven days after eggs were mapped, they were evaluated and the fate of each recorded.
For insectary procured eggs, tomato leaves were placed overnight in water pics inside a wire cage (42 by 44 by 92 cm) containing approximately 15 gravid M. sexta moths. The following morning, all but five eggs were removed from each leaf and a detailed map of egg locations drawn on a paper tag secured to the base of each leaf. Leaves in water pics were then taken to the field and secured with rubber ties to five randomly selected tomato plants in each plot. After two days, leaves were removed from the field, placed in plastic bags then treated in the same manner as field collected eggs.
A reference collection was made of bollworms and hawk moths as well as the their egg and larval parasitoids from within experimental plots. Identifications were verified by Ken Ahlstrom and David Stephan of North Carolina State University, Raleigh.
Sampling – Larval Parasitism. On six dates in 2003 (9 July, 16 July, 24 July, 30 July, 6, August and 13 August) and six dates in 2004 (9 July, 15 July, 22 July, 29 July, 4 August and 10 August) field populations of larval hawk moths (Manduca spp.) were monitored for parasitism by Cotesia congregata (Say) (Hymenoptera: Braconidae). Each plant in every plot was examined and the total number of hawk moth larvae, parasitized and not, recorded. Larvae were considered parasitized if C. congregata cocoons were present on the dorsum.
Sampling – Habitat Percent Cover. In 2003 habitat borders were weeded and dead transplants replaced. Although percent cover data were not taken, the habitat contained every plant species from the original seed mix. In 2004, habitat plots were not weeded, therefore on August 9-10, 2004 habitat borders were sampled to determine what the habitat composition was in the presence of weed competition. Percent cover of habitat plants only within each 1 m quadrat was recorded on three sides of each treatment plot. The values for all treatment plots were averaged for an estimate of percent cover for all habitat plantings. Because none of the habitat plants were not present in control plots, percent cover data were not recorded.
Data Analysis. Means for egg fate and larval parasitism was calculated per plot, per year and compared using analysis of variance (PROC MIXED, SAS Institute 2002).
For Objective 1:
In 2003, all ten advertised seed species were present in Company 1 samples, while in 2004, three of the ten advertised species were absent (Table 1). In 2003, the non-advertised species Mexican Hat and Siberian Wallflower were both present in one of three canisters from Company 1 (Table 1). In 2004, 9 different weed species were identified in subsamples from Company 1 (Table 1).
Seed abundance by percent weight varied considerably in 2003 between each of the three canisters from Company 1 was observed. Bishop’s Flower had the largest amount of variation with values ranging from 1.6-20.5% per canister (Table 1). Yarrow and Evening Primrose values were also variable, ranging from 0.6-5.6% and 3.5-13.6% per canister, respectively. Company 1 was the only seed mixture that contained an inert organic material to “help evenly distribute seed and create a mulch”, according to the manufacturers label. The amount of the material in each canister was advertised as 50.7%, although values ranged from 29.9-54.8%. In 2004, Company 1 had much less variation in subsamples (Table 1). The greatest variation was seen in Nasturtium, with values ranging from 5.9-11.9%.
Large differences were seen in the percentage of seeds by relative numerical abundance in the seed mixture from Company 1. In 2003, four seed species (Yarrow, Evening Primrose, Black-Eyed Susan, and Strawflower) made up more than 77.0% of the total percentage by relative numerical abundance (Table 1). The greatest variation was seen in Baby Blue Eyes and Strawflower with values ranging from >0.1-1.8% and 0.4-22.4%, respectively. Candytuft, Mexican Hat and Siberian Wallflower all had large variations because each seed species was found in only one container. In 2004, much less variation in relative numerical abundance was observed between subsamples from the three containers. Four seed species (Yarrow, Bishop’s Flower, Strawflower and Black Eyed Susan) made nearly 80% of the total percentage by relative numerical abundance from Company 1 (Table 1). Nasturtiums had the largest differences between containers with values ranging from 0.1-0.3%.
Germination of seeds from Company 1 was highly variable in 2003, with six of the ten species averaging germination rates below 80% (Table 1). All Strawflower and Angelica seeds tested failed to germinate, and were found to be non-viable after being subjected to a Tetrazolium Test. Candytuft, which was present in one of three containers, had only 0.7% germination. Yarrow had the greatest range in percent germination with values from 6.0-94.0%. Nasturtium and Buckwheat also showed large ranges in germination, with values ranging from 38.3-88.0% and 42.0-64.0%, respectively. In 2004, less variation was seen between subsamples of Company 1 seeds and only two of the seven species present averaged less than 80.0% germination (Table 1). Strawflower was the poorest performer, with values of 1.0-4.0% germination.
In both years of this study, all 12 advertised seed species were present in Company 2 samples (Table 2). However, in 2003 and 2004, respectively, there were 14 and seven non-advertised seed species in samples. Company 2 offered a consistent product with regards to relative numeric abundance, with little variation noted between years (Table 2). The Clover/ Alfalfa group accounted for greater than 70% of all seeds, when measured either by weight or numerical abundance, in both years of this study. The remainder of the advertised seed species were present in relatively low numbers. In 2004, weed species made up just over 1% of the average percent relative numeric abundance. Company 2 offered a consistent product with regards to percent germination. In 2003, only the Fennel and Caraway group demonstrated less than 80.0% germination (Table 2). In 2004, all species had greater than 80.0% germination. The seed distributor for Company 2 included information about % composition, purity and germination. Results from both 2003 and 2004 tests were consistent with manufacturers information.
In 2003, Company 3 had 15 of 16 advertised species present and one non-advertised species (Table 3). The composition of the Company 3 seed mix was relatively uniform. The seed species with the largest variation by percent weight was Evening Primrose, which was found in two of three packages, with values ranging from 0-1.0%. Of the advertised species, Sweet Alyssum and Bishop’s Flower, had values ranging from 0.9-2.4% and 1.3-2.4%, respectively. Of the 16 seed species present in the mixture from Company 3 in 2003, five species made up more than 50.0% of the seeds based on the average relative numeric abundance. The most prevalent seeds were Candytuft, Siberian Wallflower and California Poppy. In 2003, Company 3 had two of 15 species with less than 80.0% germination (Table 3). Gayfeather and Blanket Flower germination ranged from 18.0-56.0% and 68.0-82.0%, respectively.
In 2004, Company 4 had all 18 advertised species and three non-advertised species present (Table 4). In 2004, the composition of advertised species in the Company 4 seed mix was very consistent (Table 4). Blanket Flower had the largest variation in percent weight between subsamples, with values ranging from 3.5-7.7%. Considerable variation was seen in non-advertised species because seeds were found in only one of three subsamples. In 2004, the five most prevalent seed species from Company 4 were New England Aster, Yarrow, Sweet Alyssum, Candytuft and California Poppy. These species combined made up greater than 70% of the seeds based on the average percent relative numeric abundance. In 2004, Company 4 had two of 17 seed species with average germination rates below 80.0% (Table 4). New England Aster and Globe Gilia had germination ranges from 42.2-62.6% and 48.0-71.0%, respectively.
For Objective 1:
Company 1 offered an inconsistent seed mixture regarding the presence/ absence of seeds advertised in each mixture. Only 82.0% of the species are present in any given container, and there is only a 17.0% chance that a randomly selected container will have all ten advertised species present. The documented seed lot numbers indicated all seeds were from the same lot for both years of this study, however, considerable differences were seen between the two years. While all seeds advertised were present in one of the three canisters analyzed in 2003, 30% of the advertised seeds were missing from all canisters in 2004. The inconsistent results observed in Company 1 suggest poor quality analysis performed by Clyde Robin’s.
Two of the advertised seed components in the Company 1 seed mix, Yarrow and Evening Primrose, are considered weedy species. (Uva et. al 1997, Royer and Dickinson 1999 and Haragan 1991). The seed mix package states that 00.0% of contents are weeds and that no noxious weeds are present in any canister. However, in both years of this study, the claims made by this manufacturer were proven false. As a result of the weeds, growers could face increased weed pressure by these invasive weeds, which can be very difficult to control once established.
Company 2 offered a very consistent product with regards to the presence or absence of advertised seeds in the seed mixture, with nearly all seeds advertised being present. However, Fennel, one of the species advertised by this California based company, is ranked among some of the most invasive plant species by the California Exotic Plant Council (1999). In addition, Yarrow is considered an invasive weedy pest and can be difficult to control once established (Uva et al. 1997). Thus, growers planting this beneficial insect habitat might inadvertently make their weed problems significantly worse, and leave themselves open for serious problems if California adds Fennel to its list of Federal Noxious Weeds.
Company 3 offered a fairly consistent product in 2003, with only one advertised species missing. One of the advertised plants, Siberian Wallflower is currently on the Kansas Noxious Weed Seeds List (USDA-AMS 2002) and Yarrow, which is considered an invasive weed (Uva et al. 1997), could pose future weed problems for growers. Company 4 offered a consistent product in 2004 with all advertised species present and no seeds advertised in the mixture considered invasive or noxious weeds.
Presence or absence of species not advertised as being part of the seed mixtures. Two weed species were found in seeds from Company 1 in 2003, one of which, (Siberian Wallflower), is on the Kansas Noxious Weed Seeds List (USDA-AMS 2002). In 2004 ten weed species were found, one of which (Barnyard Grass) is a noxious weed in Arkansas (USDA-AMS 2002). Thus, by planting this seed mixture growers could inadvertently increase weed pressure.
In addition to unadvertised seeds being present in the seed mixture from Company 1 in 2003, all life stages of live lesser grain borer beetles (Rhyzopertha dominica (Fabricius)) were observed in all canisters upon arrival. These insects were actively feeding on seeds within packages, and as a result, greatly affect the weight and germination of these seeds. If a grower had ordered the seed mixtures and left them unopened for a period of time before planting, it is likely that few if any seeds would germinate once planted. In 2004, all canisters from Company 1 arrived insect pest free.
In 2003, Company 2 had relatively few weeds. The seed distributor indicated that 4.4% of their total mixture were weeds and other crop seeds, although the ten weed species recorded had a combined weight of less than 1.0%. Three weed species, Orchard Grass, Tall Fescue and Chess are listed as noxious weeds in multiple states, although the seed distributor for Company 2 indicated in paperwork accompanying seeds that no noxious weeds were present. In 2004, few weed seeds were observed and no species found was listed as a noxious or invasive weed.
Company 3 offered a consistent product, with few weeds or debris. Siberian Wallflower, an advertised seed in this mixture, is on the Kansas list of noxious weeds (USDA-AMS 2002). One unadvertised species, Evening Primrose, was present but because of the invasive nature of this plant, could end up becoming a serious problem for growers (Haragan 1991).
The seed mixture from Company 4 had little debris and few weed species. Siberian Wallflower, advertised as being in the seed mixture, is listed on the Kansas list of invasive species (USDA-AMS 2002) and one of the weed species, Yarrow, can be invasive and could pose problems for growers (Uva et al. 1997).
Consistency of composition between containers of the same seed mixtures. Percent by weight. In 2003, the average percent weight of each of the seed species from Company 1 was inconsistent between canisters. The seed distributor printed a breakdown of the contents on the side of each canister, which state that 48.9% of the contents were seeds and that none of the 10 species are present in quantities greater than 5.0% of the total mixture (CRSC 2003). However, in 2003 and 2004, 50.0% and 57.0% of the species were present in greater than the advertised 5%, respectively. Company 1 also indicated that 50.7% of the total weight was “inert organic material to help evenly distribute seed and create a mulch” (CRSC 2003). Growers who ordered this product expecting to receive 170g of seeds, may be disappointed.
It is possible that some discrepancies in the average percentage by weight in 2003 were due to the presence of live lesser grain borer beetles, which seemed to feed on the larger seeds (Buckwheat, Nasturtium and Angelica). In 2004, less variation was seen between canisters and no insects were observed.
Little variation between years was observed in advertised species in Good Bug Blend. By far, the greatest number of seeds based on percent weight was the Clover/ Alfalfa. Because the majority of seeds in this Clover/ Alfalfa group were coated, a tremendous amount of weight was added. This could pose problems if growers ordered seed based on a seeding rate that did not take this into account.
Due to the competitive nature of some of the plants in this seed mixture, future management problems could arise for growers. A study by Forehand (2004) found that in experimental plots after one year of growth, Clover, Yarrow and Fennel were the only plants remaining in all plots, of the fourteen original species transplanted.
Company 3 does not offer the consumer any information other than the species advertised in the seed mixture. They offered a consistent product, with little variation in percent by weight noted between the three analyzed packets.
Company 4 did not offer any information other than the names and species of seeds present. The average percent by weight varied greatly and could pose a problem if a grower was expecting a roughly equal distribution of seed species.
Percentage by relative numerical abundance. In both years of this study, a considerable amount of variation in percent relative numerical abundance was observed in seeds obtained from company 1. In 2003, five of the 10 advertised species averaged greater than 90% of the total percentage of seeds and large variations between canisters was recorded. In 2004, four species made up nearly 80% of the total percentage of seeds by relative numeric abundance. This could be a disappointment for growers if they were expecting a roughly equal distribution of seeds.
In both years of this study, the Clover/ Alfalfa group clearly made up most of the seed mixture from Company 2 based on the percent relative numerical abundance.
Based on the three seed packets analyzed in 2003, Company 3 offered a consistent product with regards to the average percent by numerical abundance and little variation was noted between the packets. Of the 16 advertised seeds, five species (Sweet Alyssum, Baby Blue Eyes, Candtuft, California Poppy and Siberian Wallflower) made up greater then 50% of the total percentage of seeds. Because the seed distributor does not give the consumer any information about the percent composition, a grower might assume a relatively equal distribution of seeds between the 16 species. Clearly this is not the case regarding percent weight or relative numeric abundance.
The seed distributor for Company 4 also failed to provide consumers with expectations of their seed mix. Again, if a grower was expecting a roughly equal distribution of seeds, they might be disappointed to learn that five species make over 70% of the total mix by percent relative numerical abundance.
Percent Germination. Poor germination of Company 1 seeds was observed in 2003, most likely due to the presence of live seed-feeding beetles in all three canisters. In addition to direct seed damage by beetle feeding, high levels of fungal infestation were observed during germination tests with these seeds. These fungi are likely the result of the nutrient-rich insect frass left behind from foraging within each canister or physical injury to the seeds themselves by the beetles. Probably because of a lack of pest insects, germination was higher in 2004, likely attributed to. However, in seven of 10 advertised species present, two had average percent germinations below 80% germination.
In both 2003 and 2004, Company 2 demonstrated good germination, with one plant group in each year having lower than 80% germination. In 2003, the company also included a copy of the percent composition, germination and hard seed, date tested and country or state of origin of seven of the fourteen plant groupings. All but one species met or exceeded the results provided by Peaceful Valley.
Seed mixtures obtained from Companies 3 and 4 demonstrated good germination with only two species demonstrating less than 80% germination.
For Objective 2:
Habitat type had a significant impact on the total abundance and diversity of insects found in sample plots for each of the calculated indices (see Table 3 for statistics). Of all the potential habitats studied, Border Patrol™ generally had the highest overall diversity for the index values calculated (Table 3). Of the cut flower/herb plantings, Celosia had the highest overall diversity and abundance for Simpson’s Index, Shannon’s Index and Hill’s N1 and N2 diversity numbers (Table 3). With the exception of species evenness, fennel had significantly lower index values compared to all other plant communities studied (Table 3).
Beneficial parasitoid diversity was significantly affected by habitat type for all of the index values (Table 4). Good Bug Blend and Border Patrol™ had the highest diversity and richness index values for beneficial parasitoids, but the lowest species evenness values. In general, fennel had the lowest diversity and richness values for beneficial parasitoids but the highest species evenness.
Four of the six abundance and diversity index values for the beneficial predator feeding group were significantly influenced by habitat type (Table 4). Celosia and Good Bug Blend had the highest beneficial predator index values for the cut-flower/herb and commercial mixtures, respectively, and fennel had the lowest index values.
Herbivore crop pest diversity indices were all significantly influenced by habitat type (Table 4). For four of the six index values calculated for herbivore crop pests, Border Patrol™ and Good Bug Blend were significantly higher than all other habitat types, while fennel had the lowest index values.
None of the diversity index values were significantly affected by habitat type for the mixed parasitoid feeding group (Table 4). Only species richness was significantly affected by habitat in the non-crop parasitoid feeding group. Only Hill’s N2 and species richness index values were significantly affected by habitat for inconsequential predators. Overall, fennel had the lowest Hill’s N2 and species richness index values for inconsequential predators. Habitat significantly affected species evenness and richness for non-crop pests. The three commercial mixes had the highest non-crop pests index values, while fennel had the lowest index values overall.
The only diversity value for pollinators that was significantly affected by habitat was species richness, in which Border Patrol™ and Beneficial Insect Mix had the highest index values, and fennel the lowest (Table 4). Three of the abundance and diversity indices for the decomposer/fungal feeder group were significantly altered by habitat type (Table 4). There was no significant difference in the decomposer index values between the three commercially available seed mixes, although Border Patrol™ generally had the highest values. Fennel had the lowest overall index values of all habitat types for decomposers.
Moth feeding activity varied significantly among the various beneficial insect habitats (Table 5). The highest mean number of noctuid moth flower visits per minute was recorded in Border Patrol™, while the lowest values were in Good Bug Blend, Zinnia and Beneficial Insect Mix. Border Patrol™ had significantly higher mean hawk moth visits.
Habitat type significantly altered the mean number of carabid beetles collected in pitfall traps (Table 6). The numerical trend indicated Good Bug Blend and fennel had the highest values, while Celosia and Beneficial Insect Mix had the lowest. No significant difference was seen in the mean number of spiders collected in pitfall traps placed in the habitats.
For Objective 2:
Border Patrol™ was chosen for this study because it offered the greatest variety of flower types compared to other commercial seed mixtures. The Border Patrol™ seed mixture had high diversity and evenness of beneficial parasitoids, but also had the greatest abundance and diversity of crop feeding herbivores, mixed parasitoids, decomposers/ fungal feeders, and it also attracted the highest number of pest moths of the six habitats tested. Evening primrose, the largest plant in this mixture, has large cup-shaped flowers with long, tubular corollae that open at dusk and are accessible to adult Lepidoptera (Brickell and Zuk 1997). Because Border Patrol™ harbors comparatively high crop pest populations and comparatively high levels of pest moth feeding were observed in this habitat, planting it near crops may actually increase pest insect populations.
Good Bug Blend was chosen for this study because of the high proportion of plant species with small, easily accessible nectaries within flowers. This type of floral structure is purported to benefit small parasitoids (Colley and Luna 2000, Leius 1960, Luna and Jepson 2002, Patt et al. 1997, Wäckers 2004). In this study Good Bug Blend harbored high abundance and diversity of beneficial predators, parasitoids, and ground beetles. Since this seed mixture included plants with relatively small, shallow flowers, large pollinators and lepidopteran pests were apparently less able to feed. Along with Border Patrol™, Good Bug Blend also harbored the highest abundance and diversity of crop-feeding herbivores.
Beneficial Insect Mix was chosen for this study because the plant species present in this seed mixture represented “showy” types of flowers typically associated with cut-flower production or gardening. Lepidopteran pests were not highly attracted to this habitat. Because of the large number of plant species found in Beneficial Insect Mix, it was expected that a high diversity of insects would also be observed. High abundance and diversity values were only found for non-crop herbivores and non-crop parasitoids, and this mix ranked the lowest of the three commercial seed mixtures for numbers of beneficial parasitoids and predators. It is possible that the relatively large flowers that benefited pollinators were unable to feed microscopic (1-2 mm) Hymenoptera parasitoids. This idea is supported by the work of Patt et al. (1997), who evaluated the influence of floral architecture on two parasitic Hymenoptera.
Celosia was chosen for this study because it is commonly grown in North Carolina as a cut flower crop. Overall, these plants ranked among the highest abundance and diversity values for predators, both beneficial and those of no agronomic consequence, as well as parasitoids that demonstrate varied life histories. While Celosia was the most effective of the three cut flower/ herb plantings at attracting several different feeding groups of predators and parasitoids, the groups found were for the most part not considered useful in biological control of crop pests. The floral structure of Celosia has very tightly clustered flower heads, containing up to thousands of individual flowers (Brickell and Zuk 1997) with relatively shallow, easily accessible pollen (Moore et al. 1998). Celosia attracted intermediate numbers of noctuid moths and no hawk moths, probably a reflection of this floral structure.
Zinnia is a commonly grown cut flower in the southeastern United States (Greer 2000). The large, daisy-like flower heads are borne on solitary long stems and bloom throughout the summer months (Brickell and Zuk 1997). Zinnias, which are in the same family as sunflowers, reportedly attract various kinds of beneficial insects from many different feeding groups (DuFour 2000 and Jones and Gillett 2005). This study found these plants had some of the lowest index values of insect abundance and diversity. While well suited for a cut flower cash crop, Zinnia does not appear to be effective at attracting beneficial insect populations.
Fennel is often recommended for attracting beneficial organisms in agricultural landscapes (Dufour 2000 and Al-Doghairi and Crenshaw 1999), but recommendations for using this plant have not been based on scientific evidence. Several studies have documented feeding by parasitic Hymenoptera on fennel and other umbelliferous plants (Al-Doghairi and Crenshaw 1999, Baggen and Gurr 1998, Baggen et al. 2000, DuFour 2000, Hodgson and Lovei 1993, Maingay et al. 1991, Patt et al. 1997, Poncavage 1991). However, this study found fennel had the lowest species diversity and abundance for all indices and for all feeding groups. One explanation may be that 120-d transplants were used in this study, which did not begin flowering until late summer. Fennel had an intermediate number of noctuid moth visits, and no hawk moth visits, probably reflecting the small umbelliferous structure of the flowers. A high mean number of ground beetles were collected from fennel, possibly in response to numerous immature Lepidoptera feeding on foliage.
This study demonstrates that a wide variety of arthropods are attracted to commercially available beneficial insect habitats, not only the intended beneficials. Although beneficial insects were collected from all the plantings in this study, it is unclear whether they were feeding within or benefiting from the particular plant communities. More work is necessary to determine whether these habitat plants provide pollen, nectar, alternate hosts, or other resources to specific natural enemies that attack crop pests, and if they benefit field populations of these enemies and assist in pest management. For example, Good Bug Blend had the highest diversity of beneficial parasitoids and predators of the habitat plants tested in this study. However, Forehand (2005) found that parasitism of pest moth eggs and caterpillars was not changed when small organic tomato fields were surrounded by Good Bug Blend. This suggests that high abundance and diversity of beneficial insects in a habitat may not be a predictor of how or whether the habitat functions as a pest management tool under field conditions.
For Objective 2:
Experiment 1. In 2004, average numbers of crop parasitoids, crop predators, and pollinators observed were significantly affected by flower species (F = 6.60, df = 3, 5, P = 0.0344; F = 10.45, df = 9, 16, P < 0.0001; F = 12.43, df = 9, 16, P < 0.0001). Deleterious and non-crop parasitoids, and deleterious predators were not significantly affected by flower species (F = 1.57, df = 9, 16, P = 0.2064; F = 0.12, df = 5, 9, P = 0.9849; F = 2.99, df = 5, 9, P = 0.0731; F = 2.56, df = 1, 2, P = 0.2506). In 2005, flower species significantly affected the mean numbers of parasitoids, non-crop parasitoids, predators and pollinators (F = 41.79, df = 2, 4, P = 0.0021; F = 27.45, df = 4, 8, P < 0.0001; F = 9.08, df = 4, 8, P = 0.0045) but not deleterious parasitoids, or deleterious predators (F = 2.86, df = 3, 6, P = 0.1267; F = 9.74, df = 1, 2, P = 0.0891). Pollinators and deleterious parasitoids were affected by time of day observations were made (F = 12.69, df = 1, 10, P = 0.0052; F = 9.86, df = 1, 10, P = 0.0105) while crop parasitoids, non-crop parasitoids, crop predators, deleterious predators were not (F = 1.16, df = 1, 6, P = 0.3235; F = 3.19, df = 1, 10, P = 0.1042; F = 0.16, df = 1, 10, P = 0.6966; F = 0.70, df = 1, 4, P = 0.4487). The interaction between time of day and flower species significantly affected pollinators, deleterious parasitoids, and crop predators (F = 16.58, df = 4, 10, P = 0.0002; F = 7.38, df = 3, 8, P = 0.0108; F = 8.85, df = 4, 10, P = 0.0025) but not crop parasitoids, non-crop parasitoids, deleterious predators (F = 1.00, df = 2, 6, P = 0.4207; F = 0.98, df = 4, 10, P = 0.4620; F = 0.18, df = 1, 4, P = 0.6907). In 2004, significantly more crop parasitoids were found feeding from celery than other plants, while in 2005 they fed from fennel in significantly higher numbers than from other plant species (Table 2). In 2005, non-crop parasitoids fed in significantly greater numbers from buckwheat flowers. In 2004 and 2005, crop predators fed in significantly higher numbers from fennel than the remainder of the flower species. In 2005, significantly more crop predators were present on buckwheat at 9:30 than at 12:00. In 2004, higher mean numbers of pollinators were found feeding from blanket flower, but did not significantly differ from mean number of pollinators feeding from tickseed (Table 2). Mean numbers of pollinators feeding from tickseed, fennel, yarrow, daisy, black-eyed Susan, and California poppy were approximately equal while celery, red clover, (Trifolium repens L.), and buckwheat were fed upon least. In 2005, more pollinators were observed feeding from black-eyed Susan and buckwheat than all other plant species. More pollinators were observed at both black-eyed Susan and buckwheat at 9:30 than at 12:00. The effects of replication and date on mean numbers of insects feeding from flowers in 2004 were significant for crop parasitoids (F = 3.98, df = 2, 11, P = 0.0383; F = 14.48, df = 6, 7, P < 0.0001). Replication did not effect deleterious or non-crop parasitoids, deleterious predators, crop predators, pollinators (F = 0.54, df = 2, 13, P = 0.5883; F = 0.59, df = 2, 13, P = 0.5568; F = 3.33, df = 2, 10, P = 0.0779; F = 0.23, df = 2, 17, P = 0.7948; F = 2.91, df = 2, 17, P = 0.0619). Date played a significant role in the number of pollinators and non-crop parasitoids found feeding from flowers (F = 9.16, df = 6, 13, P < 0.0001; F = 3.13, df = 6, 13, P = 0.0139) but not deleterious parasitoids, deleterious predators, or crop predators (F = 1.06, df = 6, 13, P = 0.4063; F = 2.40, df = 6, 13, P = 0.1056; F = 1.86, df = 6, 13, P = 0.1029). In 2005, no effect of replication was found for any of the feeding guilds. Week significantly affected the number of pollinators and non-crop parasitoids observed on flowers (F = 34.21, df = 5, 10, P < 0.0001; F = 7.89, df = 5, 10, P = 0.0030) but did not affect mean numbers of crop predators, deleterious predators, crop parasitoids, non-crop or deleterious parasitoids (F = 0.83, df = 5, 10, P = 0.7181; F = 2.68, df = 5, 10, P = 0.0865; F = 2.03, df = 5, 10, P = 0.1599; F = 1.31, df = 5, 10, P = 0.3356). In experiment 2 flower species significantly affected abundance of mymarids and trichogrammatids but not scelionids (F = 11.81, df = 5, 10, P = 0.0006; F = 13.45, df = 5, 10, P = 0.0004; F = 1.83, df = 5, 10, P = 0.1947). Height (F = 21.47, df = 2, 44, P < 0.0001; F = 25.51, df = 2, 44, P < 0.0001; F = 8.25, df = 2, 44, P = 0.0009) and the interaction between flower species and height played a significant role in abundance of mymarids, scelionids, and trichogrammatids (F = 7.24, df = 10, 44, P < 0.0001; F = 6.69, df = 10, 44, P < 0.0001; F = 4.17, df = 10, 44, P = 0.0004). The interaction between flower species and flower removal significantly affected trichogrammatids (F = 7.16, df = 5, 12, P = 0.0026) but not mymarids or scelionids (F = 0.56, df = 5, 12, P = 0.7280; F = 1.35, df = 5, 12, P = 0.3104). Flower removal and the interaction between flower removal and height significantly affected abundance of scelionids (F = 6.76, df = 1, 12, P = 0.0232; F = 6.20, df = 2, 44, P = 0.0042). Flower removal and the interaction between flower removal and height did not significantly affect abundance of mymarids (F = 1.62, df = 1, 12, P = 0.2266; F = 2.26, df = 2, 44; P = 0.1167) or trichogrammatids (F = 0.18, df = 1, 12, P = 0.6818; F = 0.41, df = 2, 44, P = 0.6672). There was a significant three way interaction between flower species, flower removal, and height for scelionids and trichogrammatids (F = 2.64, df = 10, 44, P = 0.0130; F = 2.28, df = 10, 44, P = 0.0298), but not for mymarids (F = 1.69, df = 10, 44, P = 0.1123). Among the different heights, a significant flower effect was found for mymarids, scelionids, and trichogrammatids at height 2 (flower height ) (F = 5.08, df = 5, 10, P = 0.0141; F = 4.70, df = 5, 10, P = 0.0182; F = 5.78, df = 5, 10, P = 0.0092) and height 1 (0.5 times flower height) (F =12.55, df = 5, 10, P = 0.0005; F = 3.24, df = 5,10, P = 0.0536; F = 22.38, df = 5, 10, P < 0.0001). At the height 3 (1.5 times flower height), there was a significant flower effect on abundance of trichogrammatids (F = 5.58, df = 5, 10, P = 0.0103) but not on abundance of mymarids (F = 2.56, df = 5, 10, P = 0.0965) or scelionids (F = 1.04, df = 5, 10, P = 0.4479). For Objective 2:
Experiment 1 was designed to determine which flowering plants provide floral food resources to beneficial insects. Two feeding guilds, crop parasitoids and crop predators, were considered beneficial insects because of their ability to affect agricultural pests. Other insects feeding from floral structures were recorded as farmers may assume they are beneficial because they look (to the untrained eye) similar to beneficial insects. The latter have species that may be deleterious because of their potential to reduce numbers of pollinators or spiders through predation or parasitization (e.g. Pompilidae and Chrysididae) (Triplehorn and Johnson 2005). We also recorded numbers of pollinators and non-crop parasitoids which may benefit the farm through pollination of crops or reduction of turf grass pests but play no role in crop pest management.
Results from this study show that insects belonging to different feeding guilds preferentially feed from different flower species. Direct comparison of the two study years is impossible as planting design and plant species observed differed between years. However, in both years, the same feeding guilds were affected by flower species with the exception of non-crop parasitoids. Overall trends in the frequency of feeding visits made by beneficial insects can be seen in both years. Fennel received the greatest number of feeding visits from crop predators both years and in 2005 fennel was frequented most often by crop parasitoids. In 2004, celery was visited most often by crop parasitoids. This study reinforces the observation that umbelliferous flowers which have easily accessible nectaries are often frequented by beneficial insects (Patt et al. 1997). Celery however only bloomed for three weeks in only two of the three replicates. In addition, celery is a biennial and blooms after its second year of planting. If celery blooms for only a few weeks after its second year of planting it would unlikely be a desirable component of a beneficial insectary habitat.
In 2004, few insects were found feeding from buckwheat when all observations were conducted at noon. Buckwheat tends to wilt in hot weather and does not produce nectar in the afternoon (Lee and Heimpel 2003; Olson et al. 2005). By adding a morning observation we were able to see that buckwheat was attractive to pollinators and crop predators.
This study provides preliminary recommendations about beneficial insect habitat for North Carolina growers. Siberian wallflower (Erysimum hieracifolium L.) and dame’s rocket (Hesperis matronalis L.) were eliminated from data analysis because they received so few feeding visits and therefore are likely poor choices as habitat plantings to attract natural enemies in North Carolina. Other plants, such as celery and cilantro (Coriandrum sativum L.) exhibited a short blooming period, making them unsuitable insectary habitat plants as well. In 2004, flowering was inconsistent across replications and dates causing many gaps in the data. Fennel showed promising characteristics both in terms of a long bloom period and in its ability to attract beneficial insects. Fennel, however, causes contact and photodermatitis in humans (Simon et al. 1984), can be invasive, and is listed on the California Exotic Plant Pest List (1999). Additional studies are needed on the biology and phenology of plants used in this study to determine how (if) they are useful for insectary habitat. The current findings can be a starting point for future observational studies of beneficial insect flower-feeding in North Carolina.
In experiment 2 abundance of microhymenoptera caught on sticky traps was used as an indirect indicator of relative attractiveness of each plant species to the three parasitoid families studied. The assumption was made that if flowers were attractive to microhymenoptera, a greater number would be caught at height 2 (the height of flower heads) in the treatments where flowers had not been removed. Crabgrass was chosen as the control for this study because it offered a vegetative habitat without flowers. It was assumed that if flowers were attractive, more microhymenoptera would be caught in plots containing flowering habitat than in non-flowering controls.
Each microhymenopteran family responded differently to the plants in this study (Table 3). Mymarids were found in greatest abundance at height 1 in black-eyed Susan plots. Scelionids were most abundant in cock’s comb plots at height 2. The greatest number trichogrammatids were trapped in crabgrass control plots both at height 1 and height 3. None of the flowers assumed to attract microhymenoptera belong to the family Apiaceae or Polygonaceae. These findings are significant because both fennel and buckwheat have been listed as suitable beneficial insect habitat (Maingay et al. 1991; Stephens et al. 1998; Irvin. et al. 2000; English-Loeb et al. 2003). Similar to the present findings, past work on the Small Farm Unit found abundance and diversity of natural enemies sampled from various cut flower and herb species to be lowest in plots containing pure stands of fennel and highest in cock’s comb (Forehand 2004).
Little evidence was found in this study that flower removal affected the number of wasps caught on traps. For the majority of the plant species tested, numbers of trapped microhymenoptera were the same in subplots where flowers were present compared to subplots where flowers had been removed. Only scelionids were found in greater abundance at flower height in cock’s comb plots where flowers remained intact (Table 3). This finding was similar to that of Rebek et al. (2005) who found that the removal of inflorescences from four species of flowering plants in an ornamental landscape had no effect on abundance of natural enemies collected on sticky cards. Our results differ from results of Irvin et al. (2000) who found greater abundance of the leafroller parasitoid Dolichogenidea tasmanica in buckwheat plantings with flowers present than in plantings where flowers had been removed indicating an attraction to floral structures.
Overall, the abundance of sampled microhymenoptera in this study was not different in flower plots compared to control plots. Scelionids and mymarids were found in greater numbers in a few plots containing flowering plants than in the control plots. Of these plots, mymarids were solely found in higher numbers at height 1 in black-eyed Susan and scelionids in greater abundance at height 2 in cock’s comb (Table 3). These findings suggest the flowers themselves were not attractive to mymarids. English-Loeb et al. (2003) found parasitism by mymarids to increase in the presence of buckwheat flowers. However, mymarids were caged on buckwheat putting them in close proximity to flowers. Scelionids showed preferential attraction to cock’s comb plantings at flower height indicating a possible attraction to floral structures. At height 2, trichogrammatids were most abundant in yarrow plots where flowers had been removed. Trichogrammatids were most abundant at height 1 in un-mowed control plots but were also highly abundant in mowed crabgrass control plots and buckwheat plots where flowers had been removed. This shows that while trichogrammatids appeared to be attracted to some habitats, flowers were clearly not responsible for this attraction.
Future field studies could be conducted to investigate which vegetative qualities of plants, rather than flowers, determine relative attraction to microhymenoptera. If vegetative habitat is attractive to different microhymenoptera, it would be useful to determine which habitats are preferred. In the current study, mean numbers of trichogrammatids were significantly greater within the canopy (height 1) of un-mowed crabgrass plots than in the canopy of any other plant species studied (Table 3). Using paper models of plant foliage Lukianchuk and Smith (1997) determined that female T. minutum Riley had a greater foraging success on simple rather than complex surfaces. It may be that the vegetative qualities of grass in this study exhibited a less complex structure than the foliage of the flowering plants. Trichome-density on plant surfaces could have played a role in preference of some plants over others. Keller (1987) determined that walking speed of T. exiguum was influenced by leaf-trichome form and density, with less-densely pubescent leaves permitting the fastest walking speeds. Measures of trichome-density and type are generally used to evaluate host-finding ability of parasitoids but could be important if trichomes impede location of food sources. Quantification of foliar trichomes could also be valuable since trichomes can provide shelter to microhymenoptera (Cortesero et al. 2000). In the present study, mymarids were found in greatest abundance in black-eyed Susan plots at height 1 regardless of flower presence or absence. Black-eyed Susan and cock’s comb in our plots were similar with regard to height, leaf size and shape, amount of foliage, and canopy closure. Black-eyed Susan foliage was densely covered with trichomes while cock’s comb foliage was glabrous.
In a study by Thorpe (1985) vegetation type (soybeans vs. weedy margins) was not determined to be an important factor in parasitism rates by Trichogramma minutum Riley or T. pretiosum Riley. However, height was determined to be important, with higher levels of egg parasitism by T. minutum at greater heights and higher parasitism by T. pretiosum at lower heights. Microhymenoptera in the current study were trapped at different heights relative to the height of flowers. Because different plant species bloomed at different heights, conclusions about flight-level preferences of different microhymenoptera could not be drawn. Future research could be conducted with traps placed at constant heights relative to ground-level in plots containing flowering and non-flowering plants. This would allow one to analyze flight behavior of different microhymenoptera in varied habitats relative to a constant height. In the present study, cock’s comb and black-eyed Susan bloomed at approximately equal heights. Fennel flowers were well-above and yarrow flowers well below cock’s comb and black-eyed Susan inflorescences. The effects of these height differences could have played a role in the results obtained in the present study if microhymenoptera were present in fennel plots at the approximate height of cock’s comb flowers but traps were not placed there to monitor activity.
While this study did not directly quantify attraction of microhymenoptera to habitat, some insight to habitat preference was obtained using relative measures of abundance. Microhymenoptera were not found in greater abundance in plantings containing members of the families Apiaceae or Polygonaceae. Higher numbers of only one microhymenopteran family were found at flower height in only one plant species, cock’s comb, a member of the pigweed family, Amaranthaceae. Abundance of trapped microhymenoptera varied with plant species at different trap heights for each hymenopteran family. This indicates that while habitat appears to play an important role in abundance of microhymenoptera for the most part floral food resources do not appear to be the causative agent
For Objective 3:
Egg Fate. In both years of this study the density of moth eggs was not significantly different (F = 1.12; df = 1,74; P = 0.2925) between treatment and control plots (Tables 2, 3). There was significantly lower (F = 8.57; df = 1,4; P = 0.0429) survival of moth eggs in 2004 than in 2003, primarily as a result of increased parasitism (F = 85.21; df = 1,4; P = 0.0008). Identifiable predation was a minor component of egg mortality, but unidentified predation may be part of the approximately 35-52% of the eggs that met an unknown fate.
Neither parasitism nor predation of moth eggs in tomatoes was significantly altered by the presence of beneficial insect habitat around plots (parasitism: F = 0.26, df = 1, 5, P = 0.6325: chewing predation: F = 0.62, df = 1, 5, P = 0.4665: sucking predation: F = 0.52, df = 1,5, P = 0.5036). The percentage of eggs that met an unknown fate also was not significantly affected by habitat (F = 1.55; df = 1,5; P = 0.2685).
Larval Parasitism. Larval populations of Manduca spp. were significantly higher (F = 17.77; df = 1,4; P = 0.0135) in 2004 than in 2003 (Fig. 1). This provided an opportunity to test habitat effects in larval population densities that differed by approximately six-fold. However, densities of larvae in treatment and control plots were not significantly different (F = 0.05; df = 1,5; P = 0.8292). Presence of beneficial insect habitat did not significantly (F = 2.15; df = 1,5; P = 0.2021) influence parasitism levels in either year of the study.
Percent Habitat Cover. Only six of the original fourteen species in the beneficial insect habitat were present at the conclusion of the 2004 field season. Yarrow, fennel and clover were the only species present in every plot with average percent cover estimates of 14.8%, 10.4% and 6.4%, respectively (Forehand 2005). Celery was found in two plots (0.7%), while only one alfalfa and one dill plant occurred in a single subsample of a single plot (both 0.1%).
For Objective 3:
For beneficial insect habitat to be useful in pest management there must be a net gain in beneficial insects and a net reduction in insect pests (Landis et al. 2000). Research conducted at the Center for Environmental Farming Systems in 2003 compared insects collected from six different flowering plant communities, and found Peaceful Valley’s “Good Bug Blend” to harbor the highest populations of beneficial parasitoids and predators (Forehand 2005). Of the three commercial habitat blends examined by Forehand (2005) this blend should have been the best to test for pest management in a cropping system. However, after two years of evaluating its effectiveness in reducing pest moth eggs and larval numbers, there was no significant pest reduction when the habitat was compared with millet. The beneficial insect habitat used in this study was relatively diverse and should have been resource rich when compared with the monoculture of millet, which had few apparent resources for beneficial insects. Insect pests are generally not a problem in North Carolina millet. The millet in this study was kept mowed to approximately 15cm tall, and prevented from seeding in order to simulate a grassy field border, which is the most common border on organic farms in this area.
In a separate field study in fall 2003, ‘Good Bug Blend’ was planted according to supplier’s instructions and intense weed competition resulted in effectively no habitat plants in plots by July 2004 (unpublished data, M. Kroner, North Carolina State University, Raleigh, N.C). This current study occurred under what could be considered ideal conditions for the habitat to ‘work’. Organically produced plants of each species were started in a greenhouse, then transplanted to the field in the proportion that each occurred in the original seed mixture. Habitat areas were hand weeded the first year of the study, dead transplants replaced, and habitat was irrigated both years as needed. However, weeding was not done in habitat borders in 2004 and by the end of the field season the only habitat plants present in all plots were yarrow, fennel and clover. Despite the differences in plant composition of habitat borders, results of this study were the same in both years.
Peaceful Valley recommends planting 1-5% of farmland for “good results” (Anonymous 2004). The habitat borders in this study comprised approximately 36% of the total area of treatment plots and should have been more than sufficient to see a treatment effect.
Several factors were considered when determining plot size for this experiment. The effect of scale on experimental results has been a point of contention in entomology and ecology with no prevailing conclusions coming from the mixed results the literature (eg. Bommarco and Banks 2003 and Bengtsson et al. 2005). It seems the scale of the experiment should reflect the scale of the questions being asked. Large scale questions should be tested with large scale experiments. Likewise, field level questions should also be conducted at an appropriate scale. Since habitat manipulation at the level advocated by the suppliers of beneficial insect habitat is clearly at the field scale, plots were sized accordingly in this study. Plot size fairly reflected the scale of tomato production by North Carolina organic growers. Most growers use three or more staggered plantings, each of which are approximately the size of plots in this study.
One consideration in assessing beneficial insect habitat is whether it acts as a “source” or a “sink” for natural enemies (Carmona and Landis 1999). In theory, beneficial insects are intended to utilize resources within a habitat area as needed, but then move into a nearby crop to manage pest populations. However, if the habitat were too attractive and resource-rich, there would be no need for beneficial insects to enter the crop. In this study it is unlikely the habitat was acting as either a source or sink. There was no treatment effect, and observed levels of parasitism in tomato were very similar to what Schmidt (1998) found in tomatoes on four organic farms in central North Carolina.
Predators clearly play an important role in agroecosystems (Barbosa and Wratten 1998, Helenius 1998, DuFour 2000). While identifiable predation appeared to be of little consequence in regulating pest moth egg populations in this tomato cropping system, it is possible that some of the roughly 35-52% of eggs that were unrecovered may have resulted from unidentifiable predators. However, it is also likely these eggs were removed in part by heavy rains or leaf contact.
The egg parasitoids (Families: Trichogrammatidae, Scelionidae) and larval parasitoids (Family: Braconidae) we evaluated in this study represent a wide range of both sizes and life histories. Based on their size, it is likely that their floral foraging behaviors differ (Patt et al. 1997). The habitat in this study was diverse enough to provide floral structures to accommodate both. Another possible carbohydrate source besides nectar is from homopteran honeydew (Idoine and Ferro 1988, Baggen and Gurr 1998). Because aphid (Homoptera: Aphididae) colonies were present on tomatoes within all plots, it is possible that parasitoids and parasitism levels benefited regardless of the resources present in the beneficial insect habitat.
Because neither egg nor larval parasitoids appeared to be assisted by the habitat surrounding tomato plots, the results of this study can be generalized to a large segment of the agriculturally important parasitoids. Clearly, more work needs to be done to evaluate the effectiveness of beneficial insect habitats. It is also clear that the mere presence, or even increased abundance, of beneficial insects in specific plant communities does not mean that those plants will aid pest management in nearby crops. Commercial suppliers of beneficial insect habitat should bear this in mind when making claims about the value of their products.
The authors have worked very closely with organic growers for many years and most, if not all, feel very strongly that a strip of diverse flowering plants surrounding their production area or specific crops encourages beneficial insects and reduces pest insect pest problems. The intent of this study was to determine if this view is correct. Bengston et al. (2005) observed that the relatively large non-cropped areas (field margins, field borders, hedgerows, etc.) are important refuges for many organisms. We agree with this observation and conclude that the surrounding, highly plant-diverse, unmanaged habitat, surrounding organic farms is more important to pest and beneficial insect ecology than planting a strip of flowering plants. Planting flowering strips alone, without the support of other nearby refuges, is unlikely to provide the economic return needed to offset the cost of establishment and maintenance.
Educational & Outreach Activities
Forehand, L.M., D.B. Orr and H.M. Linker. 2006. Insect communities associated with beneficial insect habitat plants in North Carolina. Environ. Entomol. 35: 1541-1549.
Forehand, L.M., D.B. Orr and H.M. Linker. 2006. Evaluation of a Commercially Available Beneficial Insect Habitat for Management of Lepidoptera Pests in Organic Tomato Production. J. Econ. Entomol. 99: 641-647.
Witting, B.E., D.B. Orr, and H.M Linker. Attraction of Insect Natural Enemies to Habitat Plantings in North Carolina. J. Entomol. Sci. (accepted with revision).
Orr, D., H.M. Linker, L.M. Forehand. 2006. The Use of Commercially Available Beneficial Insect Habitat for Sustainable Insect Pest Management. Plow Sharing Newsletter, September-October, 2006. pp. 10-13.
L.M. Forehand. 2004. Evaluation of commercial beneficial insect habitat seed mixtures for organic insect pest management. North Carolina State University, Raleigh. 109 pp.
Witting, B.E. 2006. Assessment of Beneficial Insect Habitat Plants for North Carolina Organic Crop Production. North Carolina State University, Raleigh. 86 pp.
The results of this work have been presented to stakeholders through a variety of means. We have received a significant amount of feedback from these stakeholders, who were genuinely appreciative of the work we did, and the workshops that have been provided. Results have been presented in a variety of forums for growers and extension agents. These include:
A whole day workshop on Beneficial Insect Habitat and Release Strategies. A “Seasons of Sustainable Agriculture Series Workshop”. CEFS, Goldsboro, July 17 2006.
A half-day workshop on Enhancing Biological Control in Organic Agriculture, as part of the Carolina Farm Stewardship Association (CFSA), annual Sustainable Agriculture Conference, Durham, Nov. 4-6, 2005.
A whole day workshop on Biological Control, Beneficial Insects and Beneficial Insect Habitat, as part of the USDA 4th National Small Farm Conference, Greensboro, NC, Oct. 17-19, 2005.
A presentation on Beneficial Insects and Beneficial Insect Habitat was given at the Center for Environmental Farming Systems (CEFS) Field Day, July 28, 2005.
A half-day workshop on Beneficial Insects and Beneficial Insect Habitat, as part of the Carolina Farm Stewardship Association (CFSA), annual Sustainable Agriculture Conference, Asheville, Nov. 12-14, 2004.
A 3 hour evening workshop on Beneficial Insect Habitat, as part of the Enhancing Sustainability Workshop Series, Chatham County Extension Center, Oct. 18, 2004.
In addition to grower and agent attended workshops and meetings, results have also been presented at the following scientific meetings:
D.B. Orr, and H.M. Linker. Can beneficial insect habitat really contribute to organic insect management. Southeastern Branch, Entomological Society of America, Annual Meeting, Mar. 5-8, 2006, Wilmington, NC. (10 minute talk).
D.B. Orr, and H.M. Linker. Can beneficial insect habitat really contribute to organic insect management. Entomological Society of America, Annual Meeting, Nov. 6-9, 2005, Fort Lauderdale, FL. (10 minute talk).
B. Witting, D.B. Orr, and H.M. Linker. Insectary plants for beneficial insect habitat in North Carolina. Entomological Society of America, Annual Meeting, Nov. 6-9, 2005, Fort Lauderdale, FL. (10 minute talk).
L.D. Jackson, D.B. Orr, and H.M. Linker. Beneficial and insect pest populations in conventional and organic cotton, and organic cotton with habitat. Entomological Society of America, Annual Meeting, Nov. 6-9, 2005, Fort Lauderdale, FL. (10 minute talk).
D.B. Orr, and H.M. Linker. Can Beneficial Insect Habitat Really Contribute To Organic Insect Management? Conference Entitled “Transitioning to Organic Agriculture: Ecology, Economics, and Marketing, Aug. 29-31, 2005, Wooster OH. (20 minute talk).
Forehand, L.M., D.B. Orr, and H.M. Linker. 2004. Evaluation of Beneficial Insect Habitat for Organic Farms. California Conference on Biological Control IV, July 13-15, 2004. (poster presentation).
All objectives of this project were met, and pertinent information was delivered to primary audiences through extension workshops, and scientific publications. An immediate outcome of this project is that farmers have been provided with guidance on whether to purchase commercial beneficial insect habitat mixes. There was a great deal of interest in the results of this project at the workshops that were presented. We should observe a change in acceptance by growers of the organic dogma that simply providing flowering plants will enhance the actions of beneficial insects. This can be measured through interviews with growers, farm visits, and discussion at extension meetings. The PI’s are regularly involved in these activities already. Although no printed educational materials were developed as a result of this project, workshops and posters to accompany the workshops and a scientific meeting were developed, and are on display at the Center for Environmental Farming Systems, Goldsboro, NC
There were two unexpected outcomes in this study: First was the lack of efficacy of commercial mixes of beneficial insect habitat. The second was the intense competition of weeds with habitat plants. These outcomes have prompted further research into developing a better understanding of what components need to be present for beneficial insect habitat to be effective.
An immediate outcome of this project is that farmers have been provided with guidance on whether to purchase commercial beneficial insect habitat mixes. Pertinent information on this subject was delivered to primary audiences through extension workshops, and publications. There was a great deal of interest in the results of this project at the workshops that were presented. Approximately 225 farmers total were in attendance at the workshops.
One recommendation from this work is that farmers not blindly accept the organic dogma that simply providing flowering plants will enhance the actions of beneficial insects.
Areas needing additional study
Clearly, more work needs to be done to evaluate the effectiveness of beneficial insect habitats. Specifically, work should continue to determine which flower species actually provide resources to beneficial insects that attack crop pests. This could be done through direct observation or destructive flower sampling. Competition of habitat plants with weeds is another critical area that should be studies. Plots in the studies presented in this report required continual weeding to maintain habitat plants. To be practical for farmers, sowing methods for the plants should be relatively easy, and the plantings should be maintenance free.