Potential impacts of orchard pesticides on Tetranychus urticae: A predator-prey perspective

Tetranychus urticae Koch is a highly polyphagous pest that is notorious for developing resistance to pesticides. In many perennial cropping systems, integrated mite management relies on the conservation of natural enemies, especially phytoseiid mites, to prevent outbreaks. For successful conservation, it is important to understand non-target effects of pesticides on both spider mites and their key natural enemies, allowing producers to choose pesticides that do not selectively favor T. urticae over its natural enemies. Here, we examine lethal and sublethal non-target effects of common orchard insecticides and fungicides on T. urticae in laboratory assays and compare these effects to previous work with its most important predator in Washington orchards, Galendromus occidentalis (Nesbitt) (Phytoseiidae). In all cases, materials were either less harmful to T. urticae or were equally harmful to both species. Pesticides that were minimally harmful to T. urticae, but highly harmful to G. occidentalis included neonicotinoids (acetamiprid, thiacloprid, imidacloprid) and novaluron. The diamides (chlorantraniliprole, cyantraniliprole, flubendiamide) had minimal effect on both species. Some pesticides (lambda-cyhalothrin, spinetoram, spirotetramat) were highly toxic to both predator and prey. While the latter category may not cause immediate outbreaks, the ability of spider mites to develop resistance more quickly than their natural enemies indicates that these materials should be used with caution. This study emphasizes the importance of studying the non-target effects of pesticides on secondary pests and their biological control agents to provide a more detailed insight into conservation biological control.