Evaluation of Beneficial Insect Habitat for Organic Farms

Evaluation of Beneficial Insect Habitat for Organic Farms

Summary

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
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.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Accomplishments to Satisfy Objective 1: A very wide variety of insects were attracted to the different plant mixes studied. Although these samples are still being processed, preliminary examination indicates significant differences in species and numbers of insects attracted to the various mixes. These insects had a wide range of feeding behaviors. These included beneficial insects such as predators, parasitoids, and pollinators, but also plant feeding pest insects, as well as predators and parasitoids of beneficial insects. In addition to insects attracted to the plants during daylight, we also looked at insects attracted at night. Some of the flowers present in the study plots were highly attractive to night-flying pests such as hornworm and fruitworm moths.

Accomplishments to Satisfy Objective 2: Composition of samples examined for objective 1 was variable, and often included weed seeds. Germination of the seeds under lab conditions was also variable, with some seeds not germinating because of previous insect damage. The germination and purity data are currently being analyzed. A field study looking at season-long growth characteristics of selected commercial beneficial insect habitats is currently underway.

Accomplishments to Satisfy Objective 3: A field experiment to determine if surrounding tomato plots with beneficial insect habitat had any effect on the activity of beneficial insects and pests. A commercial beneficial insect habitat seed mix was used in the study. Plants were started in the greenhouse and transplanted to the field to create an optimal mix of plants, rather than depending on germination and growth in the field.. The beneficial insects primarily examined were Trichogramma wasps and Cotesia congregata, well-known parasitoids of eggs and larvae, respectively, of tomato fruitworms and hornworms. The data have not yet been analyzed, but seasonal charts of egg fate (Fig.s 1a,b) and hornworm larval parasitism (Fig. 2) do not reveal any major differences between plots surrounded by commercial habitat and those surrounded by millet. Data on pest numbers, crop damage and yield were also collected, but have not yet been analyzed.

Impacts and Contributions/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.

Collaborators: