Within-colony transmission of Microsporidian and Trypanosomatid parasites in honey bee and bumble bee colonies

Parasites are commonly cited as one of the causes of population declines for both managed and wild bees. Epidemiological models sometimes assume that increasing the proportion of infected individuals in a group should increase transmission. However, social insects exhibit behaviors and traits which can dampen the link between pathogen pressure and disease spread. Understanding patterns of parasite transmission within colonies of social bees has important implications for how to control diseases within those colonies, and potentially the broader pollinator community. We used bumble bees (Bombus impatiens Cresson) and western honey bees (Apis mellifera L.) infected with the gut parasites Crithidia bombi (Lipa & Triggiani) and Nosema ceranae (Fries et al.), respectively, to understand how the initial proportion of infected individuals impacts within-colony spread and intensity of infection of the parasites. In bumble bees, we found that higher initial parasite prevalence increased both...