Enhancing Biological Control With Insectary Plantings

Enhancing Biological Control With Insectary Plantings

Summary

• This multi-year project examined the use of beneficial insectary plantings to enhance biological control of cabbage aphid (Brevicoryne brassicae) by naturally occuring predacious hoverflies Our conclusions include:

  Insectary plantings were shown to increase abundance of predator eggs on broccoli fields, however no suppression of cabbage aphid was demonstrated.

  Insectary plants are used by both pest and natural enemy species and there is selectivity among species. Clearly this approach to conservation biological (beneficial insectary plantings) must consider multitrophic-level impacts on pests, beneficials, and hyperparasitoids across all crops occurring within the system. Appropriate scale of experimental design needs to incorporate dispersal behaviors of target species and natural enemies.

  Oviposition (egg-laying) behavior of adult entomophagous species may be a key factor limiting effective biological control.

1. To evaluate the relative attractiveness of selected insectary plants to entomophagous arthropods and key insect pests
2. To evaluate the potential of using beneficial insectary plants to enhance biological control of specific insect pests in broccoli production systems, including: the cabbage aphid complex and the worm complex.
3. To develop a multi-faceted educational program for growers and agricultural professionals on integrating beneficial insectary plantings into various kinds of farming operations to enhance biological pest control.

Objectives/Performance Targets

1. To evaluate the relative attractiveness of selected insectary plants to entomophagous arthropods and key insect pests.

2. To evaluate the potential of using beneficial insectary plants to enhance biological control of specific insect pests in broccoli production systems, including the cabbage aphid complex and the worm complex.

3. To develop a multifaceted educational program for growers and agricultural professionals on integrating beneficial insectary plantings into various kinds of farming operations to enhance biological pest control.

Accomplishments/Milestones

We have completed four experiments related to the objective of this project. This past year has been devoted to data analysis, presentation at professional meetings, and preparing manuscripts for submission to scientific journals. We have presented results at the national IPM conference and the national Entomological Society. We have four manuscripts in preparation.

Although we have not achieved successful enhancement of biological pest control using insectary plantings (as we had originally hoped), we have gained a wealth of information on the biology of key predacious hoverfly species in broccoli systems. We have also documented clear floral preferences among pest and natural enemy species. Our work supports the need for sound ecological knowledge when using insectary planting to enhance biological control, because both pest and natural enemy species can use the same resource.

Late season predation of cabbage aphids by predacious hoverfly larvae may have an important impact on the suppression of this pest and in preventing excessive contamination of broccoli heads by these pests. We have documented high numbers of predacious hoverfly eggs in broccoli prior to harvest and we have developed methods to identify the key predacious hoverfly species. In our field experiments to date, however, we have been unable to demonstrate an enhancement of biological control of aphids by planting blocks of insectary flowers either on the margin of the field or in within the fields.

We have made significant steps in understanding the key aspects of oviposition behavior of Eupeodes fumipennis, Sphaerophoria sulphuripes, and Syrphus opinator, the key predacious hoverfly species occurring in Oregon broccoli fields. There seems to be an “oviposition threshold” of approximately 50 aphids per plant that is required before the adult female hoverflies will begin to lay eggs on broccoli plants.

Collaborators: