Evidence piles up for popular pesticides’ link to pollinator problems

Pyrgus scriptura butterfly

Butterfly species in Northern California, such as Pyrgus scriptura (shown), may suffer spillover effects of local neonicotinoid pesticide use.

Alan Schmierer/Flickr (Public Domain)

The link between pollinator problems and neonicotinoids, a group of agricultural pesticides commonly associated with declines in honeybees, continues to build with two new studies published this week.

Butterflies of Northern California join the ranks of honeybees, bumblebees, moths and other organisms that may be feeling the effects of the infamous insecticides. Butterfly species in California’s Central Valley have dipped since the 1990s — around the same time that neonicotinoids were introduced. Matthew Forister of the University of Nevada and his colleagues report August 16 in Biology Letters that those two events may be linked.

Tracking 67 butterfly species at four locations for at least two decades, the researchers found that a decline in the number of species at each site corresponds most closely to increased neonicotinoid use in the area (as opposed to land development, warmer summers or other potential drivers). Individual butterfly species in areas with higher pesticide use experienced the steepest declines. The results line up with a 2015 study of European butterflies that tallied fewer species over a wider range.

Also reported this week, a team of British scientists similarly builds on earlier work in wild bees. Researchers at the University of York mapped population data for 62 wild bee species sprinkled across the United Kingdom along with neonicotinoid treatment in local oilseed rape (Brassica napus) fields over 18 years.

Wild bee declines across the U.K. have been linked to neonicotinoid use in oilseed rape fields from 1998 to 2011. Heather Lowther/Centre for Ecology & Hydrology

Within species, a population’s odds of going extinct increased with use of the pesticides, the team writes in the August 16 Nature Communications. That goes for both wild bees that forage on oilseed rape, and those that don’t — though populations of known foragers were three times as likely to disappear.

Taken together, the results add some long-term data to the idea that even though wild species aren’t pollinating neonicotinoid-doused crops, the effects of exposure may still appear at the regional and national level. 

Helen Thompson is the multimedia editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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