Evaluation of Beneficial Insect Habitat for Organic Farms

Evaluation of Beneficial Insect Habitat for Organic Farms

Summary

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.

Objectives/Performance Targets

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.

Accomplishments/Milestones

For Objective 1:
Work Accomplished to Date. A 2 year laboratory study evaluated the purity, composition and germination of three commercial beneficial insect habitat seed mixes. Regarding seed purity, Company 1 had two weed species present and live beetles (Coleoptera: Bostrichidae) were present and actively feeding on seeds, Company 2 had one weed species present and one advertised species missing and Company 3 had fourteen different weed species present and three advertised species missing. Regarding seed mix species composition, Company 1 habitat had buckwheat and nasturtium in the largest proportion by weight, while yarrow and evening primrose were in the greatest seed numerical abundance. In Company 2 habitat, the largest proportion of seeds by weight were coriander and candytuft, but candytuft and Siberian wallflower were numerically most abundant. The majority of seeds in the Company 3 seed mix by both weight and numerical abundance were clovers and alfalfa. Germination of seeds in Company 1’s mix was variable with two species having 0% germination, as a result of seed feeding by insects and pathogen growth from insect frass. The company 2 mix demonstrated good overall germination, with the exception of gayfeather. All seeds in the company 3 mix, except fennel, germinated at or above test values provided by the supplier.
Work Left to Do. A manuscript is currently being prepared for submission to Seed Technology

For Objective 2:
Work Accomplished to Date. A one year 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 Company 1 habitat plantings had the highest diversity and abundance of herbivore crop pests as well as the highest instances of Lepidoptera pests during night observations. Company 3 had the highest abundance and diversity of beneficial parasitoids and predators.
Visual observations were made in 2004 and 2005 of insect flower-feeding to assess the value to beneficial insects of 16 flowering plant species. Insects were identified to family level and categorized by their life histories (i.e. pollinator vs. predator, etc.). In both years, crop predators were observed feeding from fennel flowers in greater abundance than from any other flowers observed. Fennel also was fed upon most often by parasitoids of crop pests in 2005. Pollinators were observed feeding most often from Indian blanket in 2004 and from black-eyed Susan and buckwheat in 2005. In both years, deleterious and non-crop parasitoids and deleterious predators were not significantly affected by flower species.
A laboratory study was conducted in 2005 to determine whether flowers could increase the lifespan and reproductive capacity of two parasitoids of crop pests. An egg parasitoid species (Trichogramma exiguum) and a caterpillar parasitoid (Cotesia congregata), were placed in cages, and provided either flowers (fennel or buckwheat), honey or water. Wasps were monitored daily until all had died. Longevity was greatest in Trichogramma provisioned with honey and in Cotesia provisioned with buckwheat flowers. Trichogramma provided buckwheat lived longer than those provided fennel. Lifespan of Cotesia provisioned with fennel and honey was approximately equal. The shortest lifespan was recorded from both parasitoids when they were provided water. Total egg production was greatest in Trichogramma provided with either honey or buckwheat. Average female to male ratio over the lifetime of each female was greatest in Trichogramma provisioned with water alone, likely because of sperm limitation in wasps exhibiting greater longevity. Total average number of female offspring produced was greatest in Trichogramma provided honey or buckwheat flowers. Our results show that when Trichogramma were provided buckwheat flowers their lifespan and reproductive capacity increased. Buckwheat flowers also lead to greater longevity in Cotesia. In other words, flowers have the capacity to improve the health of parasitoids when they are forced to feed on them.
A field study was conducted in 2005 to determine the response to flowers by three families of egg parasitoids. The scelionids, trichogrammatids and mymarids are all important parasitoids of a number of crop pests. From the 16 plants that visual observations were made from, five were chosen that had the greatest numbers of feeding beneficial insects. These were planted in treatment plots, and included yarrow, cock’s comb, buckwheat, fennel, Shasta daisy, and black-eyed Susan. Crabgrass (Digitaria spp. Haller) that exhibited no obvious flowering served as a control. Flower heads were removed from half of each flower plot to determine the response of parasitoids to flowers versus the entire plant. Sticky traps were used to monitor egg parasitoids at three heights: flower height, 0.5 times flower height, and 1.5 times flower height. Results from this experiment show that parasitoids had preferences for different flower species. Also, trap height affected how many parasitoids were caught. Interestingly, the removal of flowers affected only scelionids on only one flower species. At flower height, scelionids were trapped in greater abundance in cock’s comb plots at flower height when flowers were present. Trichogrammatids were trapped in greatest abundance at 0.5 times flower height in un-mowed crabgrass plots, suggesting they too were not responding to the presence of flowers. Mymarids were most abundant at 0.5 times flower height in black–eyed Susan plots, regardless of whether flowers were present. Our results indicate that habitat plantings may attract egg parasitoids but that flowers themselves do not appear to be responsible for this attraction

Work Left to Do. A manuscript describing the first study under Objective 2 was prepared and submitted to The Journal of Economic Entomology, and a review has been received. Revisions are currently being made, so that the article can be returned to the journal. Manuscripts are also currently being prepared for the second and third studies.

For Objective 3:
Work Accomplished to Date. 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.

Work Left to Do. A manuscript describing the study under Objective 3 was accepted by The Journal of Economic Entomology, and will appear in the June issue.

Impacts and Contributions/Outcomes

The results of this work have and will be 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.
A series of three extension articles is being developed for the Center for Environmental Farming Systems Farmer Notes Series. The first of these is in review. These will be available in both electronic (web) and printed format.
Results have been presented in a variety of forums for growers and extension agents. These include:

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. 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).