Are neonicotinoid insecticides driving declines of widespread butterflies?

This study, from the United Kingdom, related butterfly population levels from 1984 to 2012 to various factors including summer temperatures, spring rainfall, and neonicotinoid use. The researchers found a strong negative association between increasing neonicotinoid use and the decline of 15 of the 17 resident butterfly species studied. As the butterfly declines were not only in agricultural fields the researcher suggested that these chemicals could be moving off-site with water and transported to surrounding habitats. This study is a correlation study and does not confirm causality. While the association found is very strong, researchers cautioned that neonicotinoids could be a proxy for another factor and that further study was warranted. Of the factors evaluated the only other association, which was positive, was between summer temperatures and butterflies.