Recent and future declines of a historically widespread pollinator linked to climate, land cover, and pesticides

Abstract

The acute decline in global biodiversity includes not only the loss of rare species, but also the rapid collapse of common species across many different taxa. The loss of pollinating insects is of particular concern because of the ecological and economic values these species provide. The western bumble bee ( Bombus occidentalis ) was once common in western North America, but this species has become increasingly rare through much of its range. To understand potential mechanisms driving these declines, we used Bayesian occupancy models to investigate the effects of climate and land cover from 1998 to 2020, pesticide use from 2008 to 2014, and projected expected occupancy under three future scenarios. Using 14,457 surveys across 2.8 million km 2 in the western United States, we found strong negative relationships between increasing temperature and drought on occupancy and identified neonicotinoids as the pesticides of greatest negative influence across our study region. The mean predicted occupancy declined by 57% from 1998 to 2020, ranging from 15 to 83% declines across 16 ecoregions. 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. This assessment underscores the tenuous future of B. occidentalis and demonstrates the scale of stressors likely contributing to rapid loss of related pollinator species throughout the globe. Scaled-up, international species-monitoring schemes and improved integration of data from formal surveys and community science will substantively improve the understanding of stressors and bumble bee population trends.

Chronic larval exposure to thiacloprid impairs honeybee antennal selectivity, learning and memory performances

“…Insects play a critical role in agriculture as pollinators, contributing to ecosystem stability through their pollination of crops and cultivated and wild plants ( Mashilingi et al, 2022 ). The widespread use of synthetic chemicals like pesticides, particularly neonicotinoids, is considered one of the most determinant factors in the decline of pollinator populations worldwide ( Rundlöf et al, 2015 ; Janousek et al, 2023 ). Neonicotinoids are the most widely used pesticides globally and are used to control a variety of sucking pests ( Elbert et al, 2008 ; Xu et al, 2022 ).…”

Bumble Bee Responses to Climate and Landscapes: Investigating Habitat Associations and Species Assemblages Across Geographic Regions in the United States of America

“…Overall, these findings suggest that developed land surrounding agricultural fields in the corn belt/Appalachian/northeast region of the USA supports diverse bumble bee assemblages. However, further research is needed to determine what is driving this relationship, be it increased floral resource diversity, nesting sites, or reduced exposure to pesticides that would typically be found in agriculturally intensified settings (Goulson et al, 2015; Rundlöf et al, 2015; Janousek et al 2022).…”

“…As bumble bees have strong species-specific associations with land use and climate variables, it is important to study both individual species responses and community responses to gain a more holistic understanding of how bumble bees will be impacted by environmental changes (Whitehorn et al, 2022). For example, imperiled B. occidentalis range-wide declines have been attributed to increasing temperatures during the warmest quarter of the year, severe drought years, and use of nitroguanidine neonicotinoid insecticides, while their occupancy is positively associated with increased forest and shrub area (Janousek et al, 2022). Meanwhile, previous research in Utah identified that bumble bee assemblage composition was highest at agricultural sites surrounded by more agricultural land cover, low temperatures, and high relative humidity, and lowest at agricultural sites with more urban land cover in the surrounding area, high temperatures, and low relative humidity (Christman et al, 2022a).…”

Montane Central Appalachian Forests Provide Refuge for the Critically Endangered Rusty Patched Bumble Bee (Bombus affinis)

“…Other possible stressors to bumble bees include drought, climate change, and neonicotinoid pesticide exposure (Soroye et al, 2020;Janousek et al, 2023). Risks associated with these stressors appear particularly pronounced for members of the subgenus Bombus, which includes multiple imperiled species such as RPBB and the western bumble bee (B. occidentalis), though it remains untested whether these species are more sensitive to climate change and pesticides relative to other bumble bees.…”

“…The causes of bumble bee decline are not clear, but one common trait across declining species is a disproportionately high occurrence of infections by the microsporidian Vairimorpha bombi (Cameron et al, 2011), which can cause colony failure (Otti & Schmid-Hempel, 2007). Other possible stressors to bumble bees include drought, climate change, and neonicotinoid pesticide exposure (Soroye et al, 2020; Janousek et al, 2023). Risks associated with these stressors appear particularly pronounced for members of the subgenus Bombus , which includes multiple imperiled species such as RPBB and the western bumble bee ( B. occidentalis ), though it remains untested whether these species are more sensitive to climate change and pesticides relative to other bumble bees.…”