I recently came across a new study by a group of friends and colleagues that blew me away. Of all the environmental pollutants and nasty things we use to kill pests, who knew that fungicides (chemicals used to kill fungus) would become a problem for bumblebee pollinators. This study:
McArt, S. H., C. M. Urbanowicz, S. McCoshum, R. E. Irwin and L. S. Adler. 2017. Landscape predictors of pathogen prevalence and range contractions in United States bumblebees. Proceedings of the Royal Society of London B 284: 20172181.
This study is part of a new generation of research looking a “non-target” effects and their mechanisms. It reminded me of an awesome figure that artist Frances Fawcett did for Monarchs and Milkweeds on the different mechanisms that two other pesticides (the general term for chemicals used to kill pests) may harm monarch butterflies. The figure ended up being one of those spare bricks that didn’t make the final cut. How do herbicides versus insecticides impact monarchs and milkweeds? Well, the former kills the latter and the latter kills the former. In plain English, herbicides kill plants (usually weeds), in this case the milkweed host plant of monarchs, while insecticides kill monarchs directly. It is likely that both are harmful to monarchs, but the mechanisms are decidedly different. As far as we know, herbicides like roundup do not directly harm monarchs, but rather eliminate milkweed from agricultural fields. How limiting milkweed is for monarch populations is currently being debated among scientists. Insecticides like the potent neonicotinoids often find their way into milkweeds along agricultural margins — only now is the data pouring in showing that even trace amounts have the potential to be harmful monarchs.
In terms of agricultural yield, on average, weeds are the biggest pest f most crops, and diseases such as pathogenic fungi are the second biggest problem, followed by insects 3rd. We have pesticides for each, and they are likely all harmful to our native butterflies. Another spare brick by photographer Ellen Woods below.