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  • Jane Shellenberger

Recent and future declines of a historically widespread pollinator, the Western bumblebee

“The acute decline in global biodiversity includes not only the loss of rare species, but also the rapid collapse of common species. The loss of pollinating insects is of particular concern because of the ecological and economic values these species provide. The Western bumblebee (Bombus occidentalis) was once common in western North America, but this species has become increasingly rare through much of its range, says a new USGS-led study. Even under the most optimistic scenario, we found continued declines in nearly half of the ecoregions by the 2050s and mean declines of 93% under the most severe scenario across all ecoregions.

Using 23 years of data, 14,457 surveys across 2.8 million km2 in the western United States, we demonstrate negative impacts of increasing temperatures and drought and identify nitroguanidine neonicotinoids* as the pesticides most impacting the formerly common pollinator, the Western bumblebee (Bombus occidentalis). The precipitous decline of this generalist species is a bellwether for loss across many taxa sensitive to environmental changes around the globe.

The Western bumblebee ranks among the most sensitive bumblebee species to heat stress.

Increasing temperatures can affect all bumblebee life stages and queens may be especially sensitive while overwintering underground.”

Excerpted from a PNAS research article by William M. Janousek, Margaret R. Douglas, Syd Cannings and Tabitha A. Graves –

* The nitroguanidine neonicotinoids are Clothianidin, Dinotefuran, Imidacloprid & Thiamethoxam



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