Big bees spread disease: body size mediates transmission of a bumble bee pathogen

Abstract

Trait variation can have important consequences for the outcomes of species interactions. Even though some traits vary as much within species as across related species, models and empirical studies typically do not consider the role of intraspecific trait variation for processes such as disease transmission. For example, many pollinator species are in decline because of a variety of stressors including pathogens, but the role of intraspecific trait variation in mediating disease dynamics is rarely considered. For example, pollinator body size could affect pathogen transmission via differences in resistance, foraging behavior and physiology. We tested effects of body size on pollinator pathogen transmission using the common eastern bumble bee Bombus impatiens in field tents, introducing an infected "donor" microcolony of large or small workers with an uninfected average-sized "recipient" microcolony and allowing bees to forage for 9-16 d. Small donor bees had nearly 50% higher infection intensity (cells/ 0.02 μL) than large donor bees, but large donor bees were twice as likely to transmit Crithidia bombi to recipient bees. Both behavioral and physiological mechanisms may underlie this apparent paradox. Compared to small bees, large bees foraged more and produced more feces; simulations showed that foraging and defecation rates together had stronger effects on transmission than did donor infection intensity. Thus, effects of bee size on contact rates and pathogen supply may play significant roles in disease transmission, demonstrating the multifaceted impacts of traits on transmission dynamics.

Mass-flowering monoculture attracts bees, amplifying parasite prevalence

“…Specifically, larger bee species and pollen specialists had higher parasite prevalence and richness. Larger bees forage over longer distances [33] and produce more faeces [51], which has been linked with parasite transmission [51]. In contrast to our findings, previous studies have found that smaller bee species [52] and smaller individuals [51] host more parasites than larger bees.…”

“…Larger bees forage over longer distances [33] and produce more faeces [51], which has been linked with parasite transmission [51]. In contrast to our findings, previous studies have found that smaller bee species [52] and smaller individuals [51] host more parasites than larger bees. More research is needed to examine how host traits related to movement ecology affect parasitism.…”

Floral shape predicts bee–parasite transmission potential

“…On each flower, we placed one 10 μl drop of inoculum using a micropipette. We used 10 μl because it is within the natural range for a single B. impatiens fecal event (7 ± 5 μl, mean ± SD) (Van Wyk et al, 2021), and we did not add sucrose because B. impatiens feces typically does not contain sugar (Figueroa et al, 2019). We did not consider other compounds that may be found in feces.…”

Developmental temperature predicts body size, flight, and pollen load in a widespread butterfly

“…The effect of warming temperatures on insect body size is of particular concern (Gardner et al, 2011) because this trait is tightly correlated with ecological function in nature. For example, larger dung beetles transfer more nutrients into soil (Stanbrook et al, 2021), larger‐bodied pollinators carry more pollen (Földesi et al, 2021) and transmit more parasites (Van Wyk et al, 2021), and larger mosquitoes can ingest a greater volume of blood (Rocha‐Santos et al, 2021). Additionally, larger insects often have higher fecundity (Honĕk, 1993), fly longer distances (Jahant‐Miller et al, 2022; Yang et al, 2016), and have higher mating success (Zhang et al, 2021) than their smaller conspecifics.…”