Final Report for GS03-028
Project Information
A field study was conducted in 2003 to evaluate three commonly grown flowers (Zinnia, Celosia and fennel) and three commercially available beneficial insect habitat seed blends (Peaceful Valley’s Good Bug Blend, (GBB) Clyde Robin’s Border Patrol™ (BP) and Heirloom Seed’s Beneficial Insect Mix (BIM)) to determine what insects were present in each of these different plant communities. Three experiments were conducted to evaluate mixes: 1) insect samples were collected using a D-vac, identified to family and evaluated by feeding guilds; 2) pitfall traps were collected to monitor ground beetle and ground-dwelling spider populations; and 3) dusk observations recorded visits by noctuid and hornworm moths. Celosia offered the largest diversity and abundance of predators and parasitoids in the flower plots, although the specimens collected were not found to be significant in the control of agronomic pests. Fennel, although not flowering had the lowest overall abundance and diversity of all flowering blocks. The BP plantings had the highest diversity and abundance of herbivore crop pests as well as the highest instances of Lepidoptera pests during night observations. GBB had the highest abundance and diversity of beneficial parasitoids and predators.
A laboratory study conducted in 2003 evaluated the purity, composition and germination of three commercial mixes: Border Patrol™ (BP), Beneficial Insect Mix (BIM), and Good Bug Blend (GBB). Regarding seed purity, BP had two weed species present and live beetles (Coleoptera: Bostrichidae) were present and actively feeding on seeds, BIM had one weed species present and one advertised species missing and GBB had fourteen different weed species present and three advertised species missing. The composition of BP found buckwheat and nasturtium to be the largest proportion by weight, while yarrow and evening primrose had the greatest seed numerical abundance. In BIM, the largest proportion of seeds by weight were coriander and candytuft, but numerically candytuft and Siberian wallflower were most abundant. The majority of seeds in GBB by both weight and numerical abundance, were clovers and alfalfa. Germination of seeds in BP was variable with two species having 0% germination, most likely due to seed feeding and pathogen growth from insect frass. BIM demonstrated good overall germination, with the exception of gayfeather. All seeds in GBB, except fennel, germinated at or above test values provided by the supplier.
A field study was conducted in 2003 and 2004 to evaluate the effectiveness of a commercially available beneficial insect habitat in decreasing pest caterpillar populations. Six pairs of organically managed tomato plots were established and Peaceful Valley’s ‘Good Bug Blend’ transplanted around the perimeter of treatment plots, while a brown-top millet border was planted around the controls. Helicoverpa zea and Manduca spp. eggs were monitored and categorized based on the fate of each egg after one week. When analyzed for the effect from year, treatment, year by treatment, date within year and treatment by date within year, the only significant difference seen was in parasitism by date within year. Plots were scouted weekly and the fates of hornworm larvae (Manduca spp.) were evaluated to determine if the beneficial insect habitat had an effect on larval parasitism by the braconid wasp Cotesia congregata. No significant difference was seen when data were analyzed for the effect from year, treatment, year by treatment and treatment by date within year for either 2003 or 2004. However, a significant difference was seen when evaluating date within year for larval populations. This study indicates that natural enemy populations were not amplified by the presence of a commercially available beneficial insect habitat.
Introduction
INTRODUCTION
Many organic growers believe 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. A variety of approaches have been examined to try to reach this goal. Growing multiple crop varieties in close proximity to one another has been referred to as intercropping, polycropping, mixed farming or interculture (Coll 1998). DuFour (2000) proposed farmscaping as a “whole-farm, ecological approach to pest management”, by utilizing “hedgerows, insectary plants, cover crops and water reservoirs to support populations of beneficial organisms such as insects, bats and birds of prey”. It is inferred from these ideas that beneficial insects are attracted to a less disturbed and diverse landscape, resulting in more pest insects being destroyed (Pickett and Bugg 1998). However, due to the complex and numerous underlying ecological mechanisms, data collection to scientifically evaluate these management techniques has proven to be very slow and difficult to interpret (Wratten et al. 1998).
To be useful for pest management, any area maintained for beneficial insect habitat must result in a net gain in beneficial insects and net reduction in pest insects (Landis et al. 2000). However, it is difficult to determine this relationship. Several characteristics should be considered when creating such a habitat, including increased quantities of pollen and/or nectar, over wintering sites, favorable microhabitats, and a source of alternate prey or hosts (Barbosa and Benrey 1998, Carmona and Landis 1999).
One approach to enhancing beneficial insects is to plant a commercially available seed mixture of insectary plants, or weedy plants (Nentwig et al. 1998, Dufour 2000). Advocates of these mixtures claim they will bring in beneficial insects, provide some resources for them, and help in insect pest management. Although some commercial seed producers list specific insects their mixture will attract, very little research exists to support this assertion. Braman et al. (2002) evaluated two commercially available seed mixtures for pest suppression in turfgrass and found numbers of beneficial arthropods in the flower strips was consistently lower than in that of the control. However, levels of predation in plots adjacent to these flower strips were significantly higher than that of the control. Nentwig et al (1998) reported that 10 years of research indicated that sown weed strips increase biodiversity in agroecosystems, while at the same time, not increasing and sometimes decreasing potential insect pest populations. There is a need for additional research to demonstrate to growers how these plants perform under variable field conditions. In addition, factors such as germination rates, and noxious weed contamination of commercial seed mixtures should be examined.
In 2000, N.G. Creamer (North Carolina State University, Raleigh, N.C.) and T. Kleese (Carolina Farm Stewardship Association, Pittsboro, N.C.) conducted an unpublished survey asking organic growers in North and South Carolina what their top ten research needs were. Survey results indicated the number one response was “insect pests”. When growers were asked to prioritize needs for resolving pest problems, beneficial insects and beneficial insect habitat were their first and second choices, respectively.
This project described in this report sought to assess the value of commercial beneficial insect habitat seed mixes in the southeastern United States. Because so little information exists on using commercial beneficial insect habitat, it is hoped this research will aid organic growers in making informed decisions about the effectiveness of this practice.
1)To monitor the communities of insects, both beneficial and otherwise, that are attracted to commonly planted cut flowers and cover crops on organic farms.
2)To examine the purity, composition, germination and growth characteristics of commercial seed mixtures sold as beneficial insect habitat.
3)Based on currently available literature, construct and evaluate a simple beneficial insect habitat designed to attract and build populations of the indicator species Trichogramma spp. and Cotesia congregata, egg and larval parasitoids, respectively, for suppression of tomato fruitworm and hornworms.
Cooperators
Research
Objective 1:
Seed Sources. All seeds were purchased in February of 2003. The three commercial habitat sources were: Border Patrol™ (Clyde Robin 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), Foeniculum vulgare var. bronze fennel, Zinnia elegans var. pastel dreams, Celosia cristata var. cockscomb amaranth and Fagopyrum convolvulis (buckwheat) (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945). 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 a greenhouse in 96-cell square plug flats (3.4 by 5.3 cm, Hummert International, 4500 Earth City Expressway, Earth City, MO 63045) filled with moistened Metro-Mix 200 potting soil (Scotts-Sierra Horticultural Products Co., The Scotts Company, 14111 Scottslawn Rd., Marysville, OH 43041). Each species was planted in separate trays, with the exception of the clover and alfalfa, which were planted in a mixture. Plug trays were placed under high intensity metal halide lights on a 12-hour photophase and watered for five minutes twice daily under a misting bed. Plants were supplementally watered as needed and fertilized once every two weeks with Omega 6-6-6 (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945). At approximately 10-25 cm tall, plugs were transplanted into plastic beverage cups (266 ml, Food Lion, LLC., Salisbury, NC 28144) with 1.3 cm holes drilled in the bottoms, and kept in the greenhouse until transplanting in 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.
This study was set up using a complete block design with selective placement of treatments. Three blocks were planted from the northeast to the southeast with the same order of treatment plots as follows: Celosia, fennel, Border Patrol™, Good Bug Blend, Zinnia, buckwheat and Beneficial Insect Mix. The first block bordered various solanaceous crops; the second block was 58.4 m away bordering various brassica crops; and the third was 38 m further and planted beside corn and clovers. A 1.5m buffer area around each plot 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 m by 2.1 m planted in three rows 76 cm apart with 30.5 cm between each transplant. Buckwheat was direct seeded on 76 cm rows, using an Earthway Seeder (Earthway Products, 1009 Maple St., Bristol, Indiana), however, it was not analyzed as part of this study because of the difficulty of sample sorting.
Transplanting design for the commercial habitat seed mixes reflected the numerical abundance of each species present in each mix (see Forehand 2005). Planting was done using plywood templates with a pair of 10.2 cm holes cut into every 0.09 m2 (Forehand 2005). For Border Patrol™, a 0.6 m by 1.5 m template was used 12 times per plot; four times lengthwise and three times across, so that each plot measured 6.1 by 1.8 m. Transplanting locations for angelica and strawflower were left blank due to 0% germination. For Beneficial Insect Mix, a 0.9 m by 1.5 m template was used 8 times per plot, four times lengthwise and two times across so each plot measured 6.1 by 1.8 m. The planting template for Good Bug Blend employed two 0.6 m by 3.0 m plywood boards to accommodate the high variability in abundance of the 14 plant species (Forehand 2005). One template was used three times while the other was used twice.
Plot Management. In April of 2003, untreated soybean meal (Wyatt Quarles, P.O. box 739, Garner, NC 27529) was applied to each plot at a rate of 78.5 kg/ha and incorporated with rakes. All plants were transplanted 15-18 May 2003 with planting templates, hand trowels and bulb diggers. All plots were then mulched with organic wheat straw. For two weeks following transplanting, any dead plants were replaced. Plants were watered as needed using pump-fed soaker hoses (Aquapore Moisture Systems, Inc., A Fiskars Co., 610 S. 80th Ave., Phoenix AZ 85043) or hand watering. Weed management consisted of hand-weeding within plot and weed eaters or lawnmowers around and between plots.
One treatment of Surround® (Engelhard Corporation, 101 Wood Avenue, Iselin, NJ 08830) was applied on 28 May, 2003 to one plot of Beneficial Insect Mix and all candytuft plants in Beneficial Insect Mix and Border Patrol™, due to a damaging numbers of spotted cucumber beetles (Coleoptera: Chyrsomelidae) at the time of transplant. In addition, each candytuft plant was covered for one week in a cheesecloth cage supported on three sides by stakes as further protection from beetle damage.
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 and aerial nets (Bioquip, 321 Gladwick Street Rancho, Dominguez, CA 90220). Sampling was conducted between 11:00 am and 2:00 pm, when insect populations 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 plants to recover, the sides of plots sampled each week was alternated so that no side was sampled more often than every two weeks. Insect samples collected were transferred into glass kill jars (Bioquip, 321 Gladwick Street, Rancho Dominguez, CA 90220) treated with ethyl acetate. Once dead, insects were placed in plastic bags (3.75 L, Ziploc®, S.C. Johnson & Co., Racine WI) and stored in a cooler until transported to the laboratory where they were placed in a freezer at –20oC.
All contents of plastic bags were later transferred to 50% ethyl alcohol, and any large plant material or seeds removed and discarded. All insects larger than 3 mm were removed from samples and placed into 125 ml wide-mouth polypropylene vials (Fisher Scientific, P.O. Box 4829, Norcross, GA 30091) containing 50% ethyl alcohol. The remaining insects, those smaller than 3mm, were placed in a 1 L beaker and the entire liquid contents brought up to 600 ml using 50% ethyl alcohol. The contents were poured into a 29.2 cm by 34.3 cm tray, then thoroughly mixed and allowed to settle so a relatively equal distribution was achieved. Three subsamples were selected from each tray by randomly placing three cut rims of 7.6 cm petri dishes (Fisher Scientific, P.O. Box 4829, Norcross, GA 30091) on the bottom of the tray, then pipetting all insects within the rim into a 125 ml plastic vial (Fisher Scientific, P.O. Box 4829, Norcross, GA 30091).
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 1 hour later. Each plot was observed three times during the hour for one minute using flashlights (One-million candle power, Garrity Industries, Inc., Madison, CT 06443) covered with red cellophane. The total number of noctuid moths (Lepidoptera: Noctuidae) and hornworm moths (Lepidoptera: Sphingidae) visiting each plot was recorded. 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 (Acarina: Araneidae), pitfall traps were placed into each of the different plant communities on seven dates in 2003: 26 June, 10 July, 17 July, 25 July, 231 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 6 cm from the top. Using a garden bulb digger, cups were randomly placed in the ground so that the upper lip of the cup was even with the soil surface. Each pitfall trap was set out and collected from the same site each week. Approximately 2.5 cm of 50% antifreeze (Honeywell International Inc., 101 Columbia Rd., Morristown, NJ 07962) was poured into the inside cup at approximately 10:00 am, then samples were collected 24 hours later in glass canning jars for transport to the laboratory. All carabid beetles and spiders were transferred into 125 ml plastic vials filled with 50% ethanol then stored until identified.
Insect Identification. Insects were observed with a binocular microscope (Bausch and Lomb, 1 Bausch & Lomb Place, Rochester, NY 14604) and all identifications made using at least one of the following sources: Bland & Jaques 1978, Borror et al. 1989, Borrer & White 1970, Flint & Dreistadt 1998, Gibson et al. 1997, Grissell & Schauff 1990, McAlpine 1981, McAlpine 1987, Mitchell 1962a. Mitchell 1962b. Mullen & Durden 2002. Stehr 1987. Stehr 1991, White 1983. Reference collections were assembled and verified by one of the following: David Stephan, Robert Blinn, Dr. Brian Wiegmann of North Carolina State University or Dr. Ken Ahlstrom.
Data Analysis. Following identification, insects were grouped by feeding guild, then Simpson’s Index, Shannon-Wiener’s Index (often called Shannon’s Index), Hill’s N1 and N2 diversity numbers, species evenness and species richness were calculated for each individual planting. These data were subjected to an analysis of variance using the General Linear Model Procedure (PROC GLM, SAS Institute 2002) and means separated using Student’s t-test (PROC TTEST, SAS Institute 2002) and LS means (SAS Institute 2002).
Objective 2:
Commercial Sources. Three seed mixes were purchased anonymously in January 2003: Border Patrol™ (BP) (Clyde Robin Seed Company, P.O. Box 2366, Castro Valley, CA 94546-0366), Beneficial Insect Mix (BIM) (Heirloom Seeds, P O Box 245, W. Elizabeth, PA 15088-0245), Good Bug Blend (GBB) (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945).
Each of the three BP packages arrived in 170 g cylindrical cardboard canisters (20.4 by 7.8 cm) with one metal and one plastic endcap. The three BIM packages contained 28.4 g of seed mixture sold in paper envelopes (12.4 cm by 10.1 cm) and GBB was packaged in brown-paper bag secured with packing tape and contained 2.27kg of seed mixture.
Seed Separation and Identification. Seeds of each mixture were separated using an air column seed separator (South Dakota Seed Blower (model 757), Seedburo Equipment Company 1022 West Jackson Boulevard, Chicago, IL 60607.), various sized sieves (CSC Scientific Co., Inc. 2810 Old Lee Hwy. Ste. 200, Fairfax, VA 22031) and hand separation. 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 for identification to the North Carolina Department of Agriculture & Consumer Services, Plant Industry Division - Seed Section.
Germination.
Germination tests were conducted on 100 randomly selected seeds of each species from each of three containers of BP and BIM and two subsamples from the one bag of GBB. If less than 100 seeds of a species were present in a mixture, 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 100 by 15 mm plastic petri dishes (Fisher Scientific, P.O. Box 4829, Norcross, GA 30091) 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 cm by 61.0 cm) to prevent excess water loss and placed into a seed germinator. Germinators were set on a 12-hour photoperiod and at 15oC, 20oC or 20/30oC (with 16-hours at 20oC). Germination testing procedures for each species followed recommendations in the Association of Official Seed Analysts – Rules for Seed Testing (2002). Each species germination requirements are listed in Appendix 1.6.
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 placed in a 1.0% solution of 2, 3, 5-triphenyl-tetrazolium-chloride (Grabe 1970) and soaked for 24-hours at 30oC to determine if seeds were viable or dead.
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)*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/ weight of individual seed)/ Total number of seeds in the container)] *100. Percent germination = (Number of germinated seeds/ Total number of seeds tested) *100. Comparison of three seed species shared between BIM and BP were analyzed with an analysis of variance (PROC ANOVA, SAS Institute 2002).
Objective 3:
Experimental Design. This study was conducted in 2003 and 2004 at the Center for Environmental Farming Systems (CEFS), Goldsboro, NC. All plot areas were pesticide free for at least three years prior to this study and were transitioning to organic certification. The study was set up using a randomized block design with selective placement of treatments. Treatment and control plots were separated by at least 45 m. The experiment was repeated at five locations on CEFS within a 2 km radius, and location as blocks. All plots were in the same location both years of the study, with the exception of one control plot 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.) plants transplanted 0.91 m apart on 1.52 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 was chosen because it represents a grass monoculture where insect diversity was expected to be low.
Crop Management. Tomato seeds (variety ‘Amelia’, Clifton Seed Co., P.O. Box 206, Dobson, NC 28341) were obtained in February 2003 and 2004. Seed coatings were removed with distilled water. Seeds were then planted into 96-cell round plug trays (3.8 by 3.9 cm, Hummert International, 4500 Earth City Expressway, Earth City, MO 63045) and filled with moistened Metro-Mix 200 potting soil (Scotts-Sierra Horticultural Products Co., The Scotts Company, 14111 Scottslawn Rd., Marysville, OH 43041). Plug trays were placed under high intensity metal- halide lights on a 12-hour photophase and watered for five minutes twice daily under a misting bed. Plants were supplementally watered as needed and fertilized once every two weeks with Omega 6-6-6 (Peaceful Valley, P.O. Box 2209, Grass Valley, CA 95945). At approximately 25 cm tall, plugs were transplanted into plastic beverage cups (266 ml, Food Lion, LLC., Salisbury, NC 28144) with 1.3 cm holes drilled in the bottoms.
Prior to transplanting in 2003, all plots were tractor tilled and left fallow for three weeks. Plots were then 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) and tilled. Soaker hoses (Aquapore Moisture Systems, Inc., A Fiskars Co., 610 S. 80th Ave., Phoenix AZ 85043) were placed along the center of each row where tomatoes would be transplanted. Each plot was then mulched with 10-15 cm of pesticide-free wheat straw, and tomatoes transplanted on 14-16 May, 2003. Tomato plants were 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 using either pump fed soaker hoses or hand watering. 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. In October 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, clover was mowed to ground level with a string trimmer and left for two weeks. 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. Prior to 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 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 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 calculated and planted accordingly in the greenhouse and transplant into the field.
Transplants were started in 96-cell square plug flats (3.4 by 5.3 cm, Hummert International, 4500 Earth City Expressway, Earth City, MO 63045) filled with moistened Metro-Mix 200 potting soil and were grown in the same manner as tomato plants. Each species was planted in separate trays, with the exception of the clover and alfalfa, which were planted in a mixture. Plants were transplanted into the field 14-16 May 2003, and watered as needed using pump-fed soaker hoses or hand watering.
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). To accommodate the 16 plant species present in the mix, two sheets of plywood (0.6 by 3.0 m) were employed as transplanting templates, with 16 pairs of 10.2 cm circles cut into each piece of plywood every 0.09 m on center (Forehand 2005). A soaker hose was set adjacent to the center of the habitat border for irrigation.
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 in control plots were mowed during the growing season and replanted in 2004.
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), gravid moths from the North Carolina State University (NCSU) Insectary were transported to field plots in plastic buckets with cheesecloth lids. Five plants per plot were randomly selected and one leaf on the upper third of the plant was used for caging. A cheesecloth bag (22 by 43 cm) with three to six moths was secured overnight on the selected leaf., The following day all but five 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. Reference collections 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.
On three dates in 2004 (June 7, 2004 [44 larvae]; June 14, 2004, [10 larvae]; and June 22, 2004, [33 larvae]) all hawk moth larvae were removed from each plot by hand. Plants had not yet become established and this moth flight was earlier in the season than was expected.
Sampling – Habitat Percent Cover. In August of 2004, three-1 m quadrats were sampled on three sides of the perimeter habitat for each treatment plot and all plant species that were originally transplanted were recorded based on a percent composition. Percent cover was estimated for each habitat plant species from three locations around the perimeter of the habitat planting. The average values for all treatment plots were averaged for an estimate of percent cover for all habitat plantings.
Only six of the original fourteen species 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%).
Data Analysis. Percentage egg fate and larval parasitism data were subjected to an analysis of variance (PROC MIXED), (SAS Institute 2002).
Objective 1:
Plant community 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 2 for statistics). Of the plant communities studied, Border Patrol, generally had the highest overall diversity for the index values calculated (Table 2). Of the cut flower/ herbs, Celosia had the highest overall diversity and abundance for Simpson’s Index, Shannon’s Index and Hill’s N1 and N2 diversity numbers (Table 2). With the exception of species evenness, fennel had significantly lower index values compared to all other plant communities studied (Table 2).
Beneficial parasitoid diversity was significantly affected by habitat type for three of the index values (Table 3). In general, fennel had the lowest diversity and richness index values, but the highest species evenness values. For Good Bug Blend and Border Patrol the opposite was observed. All six abundance and diversity index values for the beneficial predator feeding guild were significantly influenced by habitat type. Celosia and Good Bug Blend had the highest index values for the cut-flower/ herb and commercial mixtures, respectively, and fennel had the lowest index values. 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. For five of the six index values fennel was significantly lower than other habitats, with the exception of Zinnia for three of the index values.
For the mixed parasitoid feeding guild only two index values were found to be significantly affected by habitat type (Table 3). Although no significant difference was seen between habitat types, fennel had the lowest numerical index values and Celosia had the highest. Only species richness was significantly affected by habitat in the non-crop parasitoid feeding guild (Table 3). Although not significant, Beneficial Insect Mix had the highest numerical index values and fennel had the lowest. Only species evenness and richness index values were significantly affected by habitat for inconsequential predators (Table 3). The overall trend found fennel to have the lowest overall index values for species richness, but the highest values for species evenness. Habitat significantly affected all abundance and diversity indices for non-crop-pest herbivores (Table 3). The three commercial mixes had the highest index values, while fennel had the lowest overall index values.
The only diversity values for pollinators that were significantly affected by habitat were species richness, in which Border Patrol™ and Beneficial Insect Mix had the highest index values, and fennel which had the lowest (Table 3). All abundance and diversity indices for the decomposer/ fungal feeder guild were significantly altered by habitat type (Table 3). There was no significant difference in index values between the three commercially available seed mixes. Fennel had the lowest overall index values of all habitat types.
Moth feeding activity varied significantly among the various beneficial insect habitats (Table 4). The highest mean number of noctuid moth visits per minute was recorded in Border Patrol™, while the lowest values were in Good Bug Blend. Border Patrol™ had significantly higher mean Hawkmoths visits, while the cutflower/ herbs (Celosia, Zinnia and fennel) all had mean values of zero.
The six flowering habitats also significantly altered the mean number of carabid beetles collected in pitfall traps (Table 5). Good Bug Blend and fennel had the highest mean beetle numbers while Zinnia and Celosia had the lowest. No significant difference was seen in the mean number of spiders collected in pitfall traps placed in the habitats. However, the numerical trend indicated Good Bug Blend and fennel had the highest values, while Celosia and Beneficial Insect Mix had the lowest.
Discussion.
Over the last few decades, the major paradigm for increasing natural enemy populations has involved diversity in agroecosystems (Banks 2003, Pickett and Bugg 1998, Barbosa 1998). Perhaps none have accepted this idea more so than organic growers. Often, they grow a large assortment of crops in a relatively small area and thus, a highly diverse system is easily adopted. In addition, the idea of naturally reducing pest pressures can often be portrayed as the “silver bullet” approach that some agriculturalists have been searching for. In addition to some commonly grown cut flowers and herbs, we evaluated three commercially available seed mixes specifically marketed for increasing beneficial insect populations. Thus, the flowering mixes chosen ranged from one with large, “showy” cut flowers to one with predominantly small flowers and an intermediate mix.
Based on anecdotes, fennel is often recommended for attracting beneficial organisms in agricultural landscapes. Several previous studies have documented the effectiveness of fennel and other umbelliferous plants for feeding parasitic Hymenoptera (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), but no recommendations for using this plant have been based on scientific evidence. This study found fennel to have the lowest species diversity and abundance for all indices and for all feeding guilds (See Table 3). However, 120 day transplants were used in this study which did not begin flowering until late summer so little insect activity would be expected. Fennel had an intermediate number of noctuid moth visits, and no hawkmoth visits, probably reflecting the small umbelliferous structure of the flowers (Table 4). A high mean number of ground beetles was collected from fennel (Table 5). Carmona and Landis (1999) reported that ground beetle populations can be conserved when they are provided with adequate moisture and shelter.
Zinnia (Family: Asteraceae) is a very well known and commonly grown cut flower in this region of the United States (Greer 2000). The large, daisy-like flowerheads are born on solitary long stems and bloom throughout the summer months (Brickell and Zuk 1997). Zinnias are in the same family as sunflowers, which reportedly attract various kinds of beneficial insects from many different feeding guilds (DuFour 2000). However, this study found these plants to be one of the lowest in terms of insect abundance and diversity (Table 3). While well suited for a cut flower cash crop, Zinnia does not appear to be effective at attracting beneficial insect populations.
The floral structure of the Celosia cristata (Family: Amaranthaceae) inflorescence is that of very tightly clustered, cauliflower-like flowerheads, containing up to thousands of individual flowers (Brickell and Zuk 1997). Each individual flower is relatively shallow, with easily accessible pollen (Moore et al. 1988). Overall, the Celosia plantings in this study ranked among the highest for insect abundance and diversity values. High values of diversity and abundance were seen for predators, both beneficial and those of no agronomic consequence, as well as parasitoids that demonstrate varied life histories. Celosia, attracted intermediate numbers of noctuid moths and no hawkmoths, again, reflecting floral structure.
The Border Patrol™ seed mixture offered the greatest variety of flower types in this study but included evening primrose. This plant has large cup-shaped flowers with a long, tubular corolla, which, as its name suggests open at dusk (Brickell and Zuk 1997). Typically, the only insects with mouthparts specialized enough to feed from these flowers are adult Lepidoptera (Borror et al. 1989). Since most pest moth species are active at night, it seems that this seed mixture might actually attract and benefit pest species. As predicted, the greatest overall occurrence of noctuid and hornworm moths was seen in Border Patrol™ (Table 4). This habitat also supported the greatest abundance and diversity of crop feeding herbivores and decomposers.
Heirloom Seed’s Beneficial Insect Mix was chosen for this study because the plant species present in this mixture represented “showy” types of flowers typically associated with cut-flower production or gardening. These flowers did prove to be attractive to large pollinators such as honey bees and bumble bees in this study. Because of the large number of plant species found in this mix, it was expected that a high diversity of insects would to be observed in it. High abundance and diversity values were only found for non-crop herbivores and non-crop parasitoids. While this blend did not attract many undesirable pest species, it also did not attract the beneficial insect populations. It is possible that the relatively large flowers that benefited pollinators were unable to feed the microscopic hymenopterous parasitoids (Patt et al. 1997).
Peaceful Valley’s Good Bug Blend was chosen for this study because of the high proportion of plant species with small, easily accessible nectaries which are purported to benefit small parasitoids (Al-Doghairi and Crenshaw 1999, Baggen and Gurr 1998, Baggen et al. 2000, Colley and Luna 1999, DuFour 2000, Hickman et al 1995, Hodgson and Lovei 1993, Luna and Jepson 2002, MacLeod 1992, Maingay et al. 1991, Patt et al. 1997, Poncavage 1991, Ruppert and Klingauf 1988). This study supports previous research in that this planting had the highest abundance and diversity of both beneficial predators and parasitoids (Table 3). Again, since this mix was composed of relatively small, shallow flowered plants, Lepidoptera were probably less able to feed and few pest moths were seen (Table 4). Good Bug Blend also supported the highest mean number of ground beetles (Table 5).
Although beneficial insects were collected from the plantings in this study, it is unclear whether they were feeding within the particular plant communities. More work needs to be done in order to demonstrate specific pollen and nectar preferences among specific natural enemies that attack specific crop pests, and whether these habitat plants benefit field populations of these enemies. Even though Good Bug Blend had the highest diversity of beneficial parasitoids and predators in this study, its presence did not affect pest caterpillar populations in an organic tomato cropping system (Forehand 2005).
Objective 2:
Seed Purity. Truth in labeling is an important issue with nonregulated seed mixtures. BP advertised candytuft as being a component in the seed mixture; however, it was found in only one of the three seed containers (Table 1.1). Although the manufacturer clearly states on the outside of each canister that no weed seeds were present, Siberian wallflower and Mexican hat appeared in two different containers and were not advertised as part of the seed mixture. Initial examination of the seed contents also led to the discovery of all life stages of seed-feeding beetles (Coleoptera: Bostrichidae) actively feeding within sealed canisters.
New England aster seeds were not present in the three BIM packets examined, although it was advertised by Heirloom Seeds as being a component in the seed mix Table 1.2). Evening primrose, although not advertised as being a component in the seed mixture, was found in two of three packets analyzed.
Peaceful Valley’s GBB did not have three of the advertised species present: rose clover, sweet clover and buckwheat (Table 1.3). In addition, fourteen weed species were identified from this mixture.
Composition by Weight. BP contained between 29.9% to 54.8% inert matter with an average value of 44.6% ± 13.0% (Table 1.1). Seeds of evening primrose, buckwheat, bishop’s flower, strawflower and nasturtium were all present in quantities greater that 5.0% by weight. Buckwheat and nasturtium seeds accounted for an average of 10.9% and 9.2% of the total weights of seeds, respectively.
High variability was seen between the three canisters of BP (Table 1.1). Percentage by weight of baby blue eyes seeds ranged from 0.0% to 3.8% and averaged 1.4% ± 2.1% and bishop’s flower ranged from 1.6% to 20.5% with an average of 8.7% ± 10.3%. In both cases standard deviations were greater than average values. Strawflower, yarrow and evening primrose also showed significant variation between packages, with averages and standard deviations of 6.4% ± 5.7%, 2.9% ± 2.5% and 7.0% ± 5.7%, respectively.
Evaluation of BIM found the percentage of seeds based on weight was fairly consistent across the three packets (Table 1.2). The greatest variation was seen in sweet alyssum, with values ranging from 0.9% to 2.0% with an average and standard deviation of 1.7% ± 0.8%. Candytuft and coriander were the two species present in the greatest quantities, averaging 14.0 ± 1.6 and 13.9 ± 3.0, respectively.
In the GBB mixture, all of the clover seeds were coated, therefore clover and alfalfa seeds were separated and categorized as one component. This generic clover category comprised over 77% of the seed mixture based on weight, and was by far the largest component present (Table 1.3). The remaining twelve species accounted for approximately 22% of the total weight of the seed mix. The daikon/ radish group and the carrot family are the two most prevalent non-clover groups at 6.45% and 4.56% of the total weight, respectively. Inert matter made up 0.83% and weed species accounted for 0.64% of the total weight of the package.
Composition by Numerical Abundance. Over 90% of BP seeds were from five seed species: yarrow (25.2%), evening primrose (22.4%), blackeyed susan (19.4%), bishop’s flower (14.2%) and strawflower (11.7%) (Table 1.1). Baby blue eyes showed the greatest variability with values ranging from 0.0% to 1.8% with an average and standard deviation of 0.6% ± 1.0%. Strawflower and nasturtium also demonstrated great variability with average values of 11.7% ± 11.0% and 0.1% ± 0.1% respectively.
The approximate percentage of seed species in BIM based on their relative abundance was fairly consistent (Table 1.2). Three seed species comprised approximately 36% of the total seed mixture based on numerical abundance: candytuft (12.8% ± 5.9%), Siberian wallflower (12.2% ± 3.5%) and California poppy (10.9% ± 0.8%). The greatest variation in numerical abundance was seen in sweet alyssum, which ranged from 3.7% to 11.2% with an average value of 8.3% ± 4.0% and in candytuft, which ranged from 9.6% to 17.9%, with an average of 12.8% ± 5.9%.
In GBB the clover group was by far the most numerically abundant at 75.69% of the total mixture (Table 1.3). The carrot family and dill are the next most common seeds present at 7.67% and 5.07%, respectively. Fennel and alyssum had the fewest numbers of seeds represented, at 0.24% and 0.53%, respectively.
Germination. Of the ten seed species that were advertised in the BP seed mixture, only four species had germination rates greater than 80%: evening primrose (98.0 ± 1.0%), bishop’s flower (93.3% ± 2.9%), baby blue eyes (91.4% ± 9.0%) and blackeyed susan (88.3% ± 0.6%) (Table 1.1). Germination between canisters was fairly consistent, with the exception of yarrow, which ranged from 6.0% to 94.0% with an average of 49.3% ± 44.0%. The two non-advertised species that appeared in seed canisters, Siberian wallflower and Mexican hat, also demonstrated poor germination, averaging 48.0% and 42.0%, respectively. Angelica and strawflower, from all three containers had 0% germination. Forty seeds from each replicate of the germination study were subjected to a tetrazolium test and were found to be dead (Table 1.4). Three samples of 50 randomly selected angelica seeds from each canister were subjected to a visual evaluation for damage from seed-feeding insects. The results demonstrated that 56.0% ± 10.6% of the seeds in each canister had significant insect damage.
Heirloom Seed’s BIM demonstrated fairly consistent germination results across the three replicates, with all but one species averaging over 75% germination (Table 1.2). Gayfeather ranged from 18.0% to 56.0% with an average of 32.0% ± 20.9%. Forget-me-not initially demonstrated poor germination, but after subjecting 40 seeds to a tetrazolium test, 100% proved to be viable (Table 1.4).
Germination tests were performed on two sub-samples of each of the species present in GBB. All species were found to be within the germination levels provided by the manufacturer with the exception of fennel, which averaged 68.0% ± 2.8% (Table 1.3). Due to initial poor germination results in chervil, tetrazolium tests were performed on 75 seeds, yielding an average of 84.0% viability. Forty seeds in one replicate of dill, which demonstrated poor germination, were subjected to a tetrazolium test, yielding an average of 90.0% viability (Table 1.4).
Discussion:
All three canisters of BP were marked as coming from the same seed lot, however, because candytuft, Siberian wallflower and Mexican hat all occurred in only one of the three packages, one might question whether the see lot was uniform throughout. Additional questions of quality analysis were raised when both immature and adult live seed-feeding bostrichid beetles were identified in all three BP canisters upon receipt. If these canisters had remained untouched until spring, it is likely germination of most seed species would have been zero.
Evening primrose was present in two of the three BIM seed packets, but was not advertised. Due to the invasive nature of this weed, its introduction onto a farm could have a significant economic impact for farmers and might even adversely affect commodity quality. In addition, since this weed begins to bloom at dusk, when moth activity is heaviest, it is possible that by planting this species growers might inadvertently increase pest pressure, rather than decrease it.
Although weeds comprised a small percentage of the total weight of GBB, a large number of weed species were present (Appendix 1.7). While none of the weeds present in the seed mixture are on the Federal (Plant Protection and Quarantine 2002) or the North Carolina Noxious Weed Lists (North Carolina Department of Agriculture 2003), introduction of any weeds onto farms could pose a significant problem for farmers. In addition, GBB had a large proportion of clovers, which could result in possible competition problems in the field. Most of the other plants in this seed mixture would not able to compete with the clovers, especially after the cool season when their growth outstrips warmer season species. Thus, it is possible that after one season a farmer may be left with only a habitat of clovers (See Chapter 3).
BP was the only seed mix selected which included an inert packing material to “help evenly distribute seed and create a mulch”. However, the website does not mention that roughly 50% of their seed mixture is inert material (Clyde Robins 2004). Thus, a grower might be disappointed at the contents upon receipt. Also, because of the inert material, the presence of live insects might be overlooked if casually examined.
BP also clearly states on the outside of each canister that no “species is present in quantities greater that 5% of the total mixture” which suggests a roughly equal distribution among the seed species. However, five of the ten seed species, yarrow, evening primrose, blackeyed susan, bishop’s flower, and strawflower were found in quantities significantly higher than 5%. Together, those five seed species account for 93% of the total number of seeds. In the field, it may be difficult to get an even stand of all species. Again, due to the invasive nature of evening primrose, growers might be inadvertently introducing a much larger weed problem.
Heirloom Seed’s supplies the common names of the seeds included, but they offer no information regarding the percent composition or germination statistics of their product. BIM offered a fairly consistent product across the three packages that were analyzed and little variation was seen when comparing the seeds by weight or by numerical abundance. There was very little inert matter and no insects present in the packages examined.
The vast majority of the seeds in GBB were clovers and alfalfa. Because all clover seeds were coated, it added a significant amount of weight and volume to the packaged seeds. Thus, a farmer might be discouraged upon arrival if they were expecting 2.2 kg of pure seed.
BP demonstrated very poor germination in the laboratory and in fact, live insects could be seen emerging from seeds while the germination tests were being conducted (Appendix 1.8 and 1.9). Insect feeding appears to be the primary cause of poor germination in some species, especially buckwheat and angelica. High levels of pathogen growth were also observed during the germination tests. It is possible that this is the result of the presence of nutrient-rich insect frass left behind from foraging within each canister or physical injury to the seeds themselves by the insects.
This study was designed to test the germination of each seed species under their individual ideal conditions. With such poor germination of some of the species in the laboratory setting, one must question how well these seeds would germinate if planted according to manufacturers recommendations. It is highly likely that the BP planting would contain only a few species, which would quickly be overtaken by the evening primrose. Because of the invasive nature of this weed, it could have significant negative impacts for farmers, not only for weed management, but also for moth pest pressure.
BIM demonstrated very good germination results for all seed species with only one of 16 species reporting less than 75%. Gayfeather, which averaged 32.0% ± 20.9%, had the lowest germination, perhaps due to the fact that many of the seeds were damaged. Thus, a grower could expect a fairly good germination and an even distribution of all the flowering types.
Peaceful Valley was the only company to provide seed germination rates with their GBB product and thus is the only company our results can be compared to. Overall, good germination was seen and our results are in line with the data provided by the manufacturer, the only exception being that of fennel.
Each of these beneficial insect habitat seed mixes undoubtedly provide some of the life sustaining products that insects, both beneficial and otherwise, need to survive in an agricultural landscape. However, all three seed mixes analyzed had species absent which were advertised as being part of the mix. All three also had species present, which were not advertised by the manufacturer. If growers are faced with increased weed pressure from a species that was introduced in one of these seed mixes or increased pest pressure from certain plants acting as food sources, they might question the additional value of these products. Clearly more work needs to be done examining the quality and effectiveness of these and other plantings. But it is our hope that this study illustrates for growers the need to evaluate each product on an individual basis and to be wary of products making promises of “silver bullets”.
Objective 3:
Egg Parasitism. 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 1, 2). 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 42-52% 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 = 0.84, df = 1, 4, P = 0.4123: 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.
Discussion
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 (See Forehand 2005). Of the three commercial habitat blends examined by Forehand (2005) this 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.
This trial occurred under what could be considered ideal conditions for the habitat to ‘work’. The seeds in the habitat blend were separated by species, and the composition of each in the blend determined (Forehand 2005). 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. Transplants that didn’t survive transplanting were replaced. Plants in both the greenhouse and the field were grown under organic conditions. Habitat areas in the field were weeded the first year of the study, and irrigated both years as needed. In a separate field study in fall 2003, when this same habitat mix was planted according to supplier’s instruction 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).
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 were very similar to what Schmidt (1998) found in tomatoes on four organic farms in central North Carolina.
A diverse community of flowering plants was transplanted around the perimeter of treatment plots at the beginning of this study (see Table 1). However, many of these species flowered in 2003 but did not appear in large numbers in 2004. In fact, the only plants seen in all plots at the end of the 2004 field season were yarrow, fennel and clover. Besides nectar, another possible carbohydrate source 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.
Predators clearly play an important role in agroecosystems (Barbosa and Wratten 1998, Helenius 1998, DuFour 2000). However, they appeared to be of little consequence in regulating pest moth egg populations in this tomato cropping system. 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. Because neither egg nor larval parasitoids appeared to be assisted by the habitat, 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.
Educational & Outreach Activities
Participation Summary:
Publications:
L.M. Forehand. 2004. Evaluation of Commercial Beneficial Insect Habitat Seed Mixtures for Organic Insect Pest Management. MS Thesis, North Carolina State University.
Outreach:
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).
"Beneficial Insect Habitat for Crop Pest Management". (A workshop by L. Forehand, L. Jackson, B. Witting, M. Kroner, D. Orr, M. Linker). Enhancing Sustainability Workshop Series, Chatham County Extension Center, Oct. 18, 2004.
“Habitat to Enhance Beneficial Insects”. (A workshop by L. Forehand, L. Jackson, B. Witting, M. Kroner, D. Orr, M. Linker). CFSA Sustainable Agriculture Conference, Asheville, Nov. 12-14, 2004.
“Beneficial Insects on the Farm”. (A poster by L. Forehand, D. Orr, and M. Linker). CFSA Sustainable Agriculture Conference, Asheville, Nov. 12-14, 2004.
Project Outcomes
This work has produced information that provides organic growers with sorely needed information on insect management. Specifically, it provides organic growers with guidance on selecting commercial beneficial habitat seed mixes, cut flowers, and cover crops to influence both beneficial and pest insect populations on their farms.
Farmer Adoption
This was not measured specifically, but there was a great deal of interest at the workshops that were presented to deliver the information from this project.
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.