Notes from the Lab
Pesticide use ia a major driver of continent-wide declines of hundreds of wild bee species in the USA
Every once in a while a scientific study comes along that improves our understanding of a topic by leaps and bounds.
While it’s well established that pesticides cause problems for bees, the scope of the problem is often what’s argued over. Are a few bees dying here and there from occasional harmful pesticide exposure, or is pesticide use driving large-scale declines at a continental scale?
And what about other aspects of agricultural intensification? In the USA we’ve been using more toxic insecticides over the past ~30 years, but the quantity of animal-pollinated crops (apples, blueberries, pumpkins, etc.) has also changed, which could provide more resources for bees. And the number of honey bee colonies has also changed, which could impact competition between managed and wild bees. Have these changes impacted wild bee distributions, or is increasing pesticide use the main stressor that’s impacting bees?
These are the topics for the eighty-first Notes from the Lab, where I summarize “Impact of pesticide use on wild bee distributions across the United States,” published in Nature Sustainability [2024] and written by Melissa Guzman and colleagues at the University of Southern California and Simon Fraser University, with some help from co-authors at the USDA ARS Pollinating Research Unit, Northern Arizona University, and researchers in Hong Kong and Germany.
For their study, Guzman and colleagues tapped into museum records, ecological surveys, and community science data from across the United States, including 178,589 unique observations from 1,081 bee species (33% of recorded bee species in the United States!) to model species occupancy between 1995 and 2015. This was a truly impressive effort resulting in data from six bee families: Andrenidae (mining bees), 220 species; Apidae (bumble bees, carpenter bees, etc.), 284 species; Colletidae (cellophane bees), 69 species; Halictidae (sweat bees), 221 species; Megachilidae (leafcutter bees, mason bees, etc.), 278 species; and Melittidae (melittid bees), 9 species.
Determining occupancy (i.e., whether a species is or isn’t present at a site) is easy when the species is collected; the physical specimen or photograph is the evidence it’s been found. But that doesn’t mean a species that isn’t collected isn’t actually there; it’s possible the collector just didn’t have enough time to find it. To account for this, the authors inferred that a visit to a site that may have detected a given species occurred only when at least one other species in the same genus was observed in the same year and county, and only for sites that fell within that species’s range …
