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Preserving Biocontrol Agents

Monday Apr 22, 2024

Natural enemies (NE) are crucial to the long-term stability of management programs. Pesticides need to be chosen not only on the basis of efficacy against the pests, but also by minimizing their effect on natural enemies. DAS provides both the effects on pests and on the key natural enemies.

The full WSU Sprayguide (accessible through the link “View full WSU Sprayguide” in the Mini Sprayguide in the model output) provides help with choosing pesticides. The efficacy of each material to control the target pest as well as secondary pests is listed in the full WSU Spray Guide under the category “Efficacy.” The category “Natural Enemies” indicates how much each pesticide negatively impacts the listed natural enemies. This list includes predatory mites (Typhlodromus occidentalis), a parasitic wasp that attacks leafrollers (Colpoclypeus florus), a parasitic wasp that attacks leafminers (Pnigalio flavipes), and aphid predators (ladybugs and lacewings). Apple rust mites, also listed, serve as food source for the predatory mite T. occidentalis early in the season and, thus, help to raise predator numbers that control spider mites later in the season. In particular, granulosis virus, oil, and Bt have low to no negative impact on natural enemies. To get more help on how to use the WSU Sprayguide, watch this video tutorial in the DAS Help Center.

Among the natural enemies of leafrollers are parasitic wasps, parasitic flies, predatory beetles, and birds. Oblique-banded leafrollers (OBLR) are predominantly parasitized by tachinid flies (Nemorilla and Nilea), both of which have their greatest impact late in the summer and which occur in virtually all orchards. Parasitic wasps also play an important role in biological control of OBLR. Pandemis leafrollers (PLR) are parasitized by wasps as well as tachinid flies. By changing your spray programs to target the young larvae of both species (which start the damage) biological control of the later instars is preserved (parasitoids don’t attack young larvae) and fewer insecticides will be required.

Enhancing Western Orchard Biological Control is a joint project of WSU, OSU, USDA-ARS, and UC to quantify the importance of natural enemies for the long-term stability of pest management programs. This project aims to (1) determine how newer pesticides affect natural enemies’ reproduction and pest consumption/parasitism; (2) characterize when key natural enemies are present and active in orchards; (3) test new and develop effective monitoring tools for natural enemies; (4) determine which generalist predators consume codling moth; (5) determine long-term economic benefits of biological control for IPM programs; and (6) apply the new knowledge to improve pest control. Tests with an attractant for lacewings, for example, revealed that these aphid predators are abundant in virtually all orchards in high numbers all season long. These findings suggest that their contribution to biological control of aphids has been underestimated. Knowing when lacewings and other natural enemies are present in orchards will help time control treatments in a way that enhances biological control as well as pesticide efficacy and, ultimately, improves pest control.

Syrphid fly adult (E. Beers)

Adult brown lacewing eating an aphid (E. Beers)

Lacewing larvae in aphid colony (E. Beers, 2005)

Colpoclypeus florus larve attacking pandemis leafroller (J. Brunner)

Colpoclypeus florus female stings leafroller larva (Stephen Ausmus, USDA-ARS)

Transverse lady beetle larva eating aphids (TFREC)

Oblique-banded leafroller attacked by a tachinid fly (N. Wiman)

More Links

Orchard Pest Management Online – Natural enemies and beneficials