Spatiotemporal overlap of pesticide use and species richness hotspots in California

The consequences of agricultural pesticide use for ecological and environmental health are partially determined by the overlap of pesticide use, in space and time, with ecologically important regions. Yet, data limitations have largely inhibited understanding of where and when such overlap occurs. Combining detailed pesticide use data from the diverse agricultural regions of California with species richness data for several taxa including birds, mammals, amphibians and reptiles, we evaluate the location and persistence of pesticide use hotspots, and where and when they align with ecologically important areas. Hotspots of pesticide use were generally located in agricultural valleys, as anticipated, yet were surprisingly ephemeral. Between 0-5 % of species richness hotspots intersected annual pesticide use hotspots depending on the focal taxa. The level of overlap also varied over the growing season, peaking for most taxa in May through July. Considering the spatial and temporal heterogeneity in both pesticide use and biodiversity is important to focus monitoring and mitigation efforts to reduce the ecological impacts of pesticide use when and where they occur.