Local habitat type influences bumble bee pathogen loads and bee species distributions

Abstract

Bumble bees (Hymenoptera: Apidae, Bombus Latreille) perform important ecological services in both managed and natural ecosystems. Anthropogenically induced change has altered floral resources, climate, and insecticide exposure, factors that impact health and disease levels in these bees. Habitat management presents a solution for improving bee health and biodiversity, but this requires better understanding of how different pathogens and bee species respond to habitat conditions. We take advantage of the washboard of repeated ridges (forested) and valleys (mostly developed) in central Pennsylvania to examine whether local variation in habitat type and other landscape factors influence bumble bee community composition and levels of 4 leading pathogens in the common eastern bumble bee, Bombus impatiens Cresson. Loads of viruses (DWV and BQCV) were found to be lowest in forest habitats, whereas loads of a gut parasite, Crithidia bombi, were highest in forests. Ridgetop forests hosted the most diverse bumble bee communities, including several habitat specialists. B. impatiens was most abundant in valleys, and showed higher incidence in areas of greater disturbance, including more developed, unforested, and lower floral resource sites, a pattern which mirrors its success in the face of anthropogenic change. Additionally, DNA barcoding revealed that B. sandersoni is much more common than is apparent from databases. Our results provide evidence that habitat type can play a large role in pathogen load dynamics, but in ways that differ by pathogen type, and point to a need for consideration of habitat at both macro-ecological and local spatial scales.

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

“…Generally, bumble bees appear adapted to consuming nutritionally relevant doses of these compounds (Jones et al, 2023), and their presence in the bumble bee diet may have implications for behavior (Villalona et al, 2020) and the epidemiology of common trypanosomal and microsporidial pathogens (Bernklau et al, 2019;Fowler et al, 2022;Palmer-Young et al, 2017;Richardson et al, 2015). Interestingly, recent work in the Appalachian ridge and valley physiographic region reported variation among habitats in the incidence of bumble bee pathogens, with trypanosome infections higher and viral infections lower in ridgetops relative to valleys (Gratton et al, 2023). The underlying drivers of this association remain unexplored.…”

Variance in heat tolerance in bumble bees correlates with species geographic range and is associated with several environmental and biological factors

“…Toward these goals, we examine heat stress tolerance variation across six species native to the Northeastern United States: B. impatiens , Bombus bimaculatus Cresson, Bombus griseocollis (De Geer), Bombus perplexus Cresson, Bombus vagans Smith, and Bombus sandersoni Franklin. These species have different but overlapping distributions and habitat preferences (Gratton et al., 2023 ; Williams et al., 2014 ) and vary in their abundance in our study region in Pennsylvania. In particular, B. impatiens is increasing in abundance, B. bimaculatus and B. griseocollis are stable or increasing, and B. perplexus , B. vagans , and B. sandersoni are more rare and potentially decreasing (Colla et al., 2012 ; Grixti et al., 2009 ; Jacobson et al., 2018 ).…”

“…For ease of viewing, significance letters in 1a represent pairwise differences among species/origin (Tukey HSD) within each caste. (B) Interspecific differences among workers (wild and laboratory‐reared bees pooled) highlighting significance values and how THS of species directly relates to their latitudinal averages of GBIF records, mean temperature (°C) across this range for June, July, and August (indicated with Xs), and habitat preferences across a forested hill to open and developed valley landscape in Pennsylvania (Gratton et al., 2023 ). Significance letters on the left of the slash represent pairwise differences (Tukey HSD) between workers of different species and letters on the right of the slash represent pairwise differences (Tukey HSD) between species from the full model, which includes workers, males, and queens in the analysis.…”

“…(Table A1). B. vagans and B. sandersoni are less common, are hard to tell apart morphologically, and occupy the same ecological niche in Pennsylvania higher elevation forests (Gratton et al, 2023) For these two models (additive and interactive), we also calculated Akaike's information criterion, corrected for small sample size (AICc), using the AICcmodavg package (Mazerolle, 2017). While these models reveal the main effects, we also conducted separate analyses for visualization purposes on subsets of the data.…”

“…In particular, B. impatiens is increasing in abundance, B. bimaculatus and B. griseocollis are stable or increasing, and B. perplexus , B. vagans , and B. sandersoni are more rare and potentially decreasing (Colla et al., 2012 ; Grixti et al., 2009 ; Jacobson et al., 2018 ). In terms of habitat, B. impatiens and B. griseocollis are more abundant in open valleys, B. sandersoni and B. vagans in the ridges, and B. perplexus and B. bimaculatus in ecotonal regions (Gratton et al., 2023 ; Williams et al., 2014 ). To understand how aspects of life history within species impact thermal tolerance and vulnerability, we examine the role of sex and caste across species, and of age, body size, and reproductive state of queens on thermal tolerance in B. impatiens .…”