How do we estimate direct and indirect effects of pesticides on BC? An overview of problems and solutions

“Reduced risk” insecticides that are being substituted for OP-products are not necessarily safe for natural enemies, and indeed may actually have both acute toxic or sublethal effects on natural enemies. Pesticides can impact natural enemies through acute mortality or through reduced longevity and sublethal effects on fertility, fecundity, or other life history parameters. In addition, while insecticide residues have been the traditional route of exposure used for laboratory bioassays with natural enemies, topical or oral intake are often more important for “reduced risk” insecticides. Here we present an overview of a two-tiered approach for laboratory bioassays to evaluate the demographic toxicity of pesticides to natural enemies that can subsequently be verified through large-block replicated field studies. The laboratory bioassays comprise a first tier test in which acute mortality is estimated, and a second tier in which life history parameters are estimated to generate population growth rates in the presence and absence of pesticide exposure. Pesticides that are either acutely toxic or generate substantial reductions in natural enemy population growth are then verified in field trials with an emphasis on large block treatments and within field replication to minimize the confounding effects of natural enemy movement and population variation.