Summary/Abstract
The western bumble bee is a once-common and integral pollinator in North America, particularly in the western United States. Several factors have been identified by previous research as contributing to the decline of this species, including rising temperatures, drought, and the widespread use of toxic nitroguanidine neonicotinoids as agricultural pesticides. This study evaluates the validity of these hypothesized causes using statistical methods based on numerous surveys of temperature, drought, and neonicotinoid use across the western United States. All of the evaluated factors were found to have a strong negative impact on bumble bee populations. The researchers then projected future bumble bee populations under three future scenarios of varying extremity. Under all of the evaluated scenarios, bumble bee populations are expected to experience extreme declines over the next several decades, posing a threat to human food systems which rely on this pollinator.