Are neonicotinoid seed treatments friendly to natural enemies? A meta-analysis

Neonicotinoid insecticides are applied to the seed of many crop species, and the percentage of seeds treated has been on the rise.  Recent research has revealed that these insecticidal seed treatments may negatively influence pollinators in agricultural landscapes, but it remains unclear whether these seed treatments pose a risk to other beneficial arthropod species, including natural enemies of crop pests. Laboratory studies show potential for neonicotinoids to adversely affect a broad range of non-target insect taxa, but these studies tend to overestimate exposure relative to field conditions. On the other hand, field studies exploring non-target effects of insecticidal seed treatments on natural enemies create more realistic conditions but often suffer from low power. To better understand the effects of neonicotinoid seed treatments on natural enemies, we synthesized data from over 16 field studies that compared natural enemy abundance in plots planted with treated and untreated seed. Collectively, these studies comprised over 35 site-years and sampled a diversity of natural enemy taxa. Using treatment means and standard deviations along with the program MetaWin 2.1, we derived effect sizes (Hedge’s d) for the difference in abundance between treated and untreated plots. We then used resampling procedures to generate bootstrap confidence intervals to test whether effect sizes differed significantly from zero. Our results will inform the larger debate about the ecological consequences of neonicotinoid seed treatments.