|Beers, Elizabeth - Washington State University|
|Mills, Nicholas - University Of California|
|Shearer, Peter - Oregon State University|
|Amarasekare, Kaushalya - Oregon State University|
|Gontijo, Lessando - Washington State University|
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2016
Publication Date: 4/22/2016
Citation: Beers, E., Mills, N., Shearer, P., Horton, D.R., Miliczky, E., Amarasekare, K., Gontijo, L. 2016. Nontarget effects of orchard pesticides on natural enemies: lessons from the field and laboratory. Biological Control. 102:44-52.
Interpretive Summary: Regulatory changes affecting types of chemical insecticides available for use in apple, pear, and walnut orchards of western North America have prompted efforts to examine effects of replacement insecticides on biological control of orchard pests. Researchers at USDA-ARS Wapato in Washington, in collaboration with scientists from Washington State University, University of California, and Oregon State University examined the effects of some newer insecticides on biological control and outbreaks of secondary pests in commercial orchards in Washington, Oregon, and California. These large field studies were supplemented with laboratory trials to examine under controlled conditions the effects of field-products on natural enemies. The studies showed that for only one predatory species did negative effects demonstrated in laboratory trials carry over to large effects in field trials. These results suggest that many natural enemies may be more resilient to insecticides under field conditions than might be predicted by laboratory trials, possibly because of colonization by natural enemies of orchards from neighboring unsprayed habitats or orchards.
Technical Abstract: The nontarget effects of insecticide programs used to control codling moth, Cydia pomonella were studied in large-plot field trials in apples, pears, and walnuts in the western United States. We sampled the abundance of natural enemies and outbreaks of secondary pests. The insecticides used in the field tests overlapped those tested in laboratory bioassays. Using these parallel lab and field studies, we examined two hypotheses: 1) pesticides found to have negative effects on natural enemy fitness in laboratory bioassays will predict reductions in natural enemy densities in the field, and 2) reductions in natural enemy densities in the field will result in outbreaks of secondary pests. We found only one clear instance, Forficula auricularia, where laboratory results documenting negative effects corresponded to a significant reduction in field studies. This same instance was the only case where a reduction in a natural enemy population was associated with a significantly increased density of a secondary pest, Eriosoma lanigerum There were instances where secondary pest outbreaks were associated with unchanged or even increased natural enemy densities. The limited number of field trials, variability in field trial conditions among years and sites, duration of the negative effect relative to sampling interval, sampling efficiency, plot size/inter-plot movement, and compensation by other natural enemies may all have contributed to the poor predictive success. Overall, the laboratory bioassays predicted a far greater negative impact than was found in the field trials.