Wild bumblebee lineage survival in response to pathogen infection and medicinal floral resources

Pathogen pressure is a suspected driver of wild bumblebee (Apidae: Bombus spp.) declines due to their impact on colony health. However, few studies have assessed the direct impact of infection on bumblebee lineage survival over multiple generations. Interestingly, Asteraceae pollen has been identified as a medicinal food source, reducing the infection intensities of significant bumblebee gut pathogens (e.g., Crithidia bombi) upon consumption. However, it is unknown if Asteraceae availability reduces infection in the field, and thus improves survival outcomes over time. Here, we assess the impacts of local Asteraceae availability on C. bombi infection and lineage survival of 20 bumblebee (Bombus impatiens) populations across two years (summers 2024 and 2025). We employ genetic mark-recapture methods for 15 B. impatiens workers per year at each site, which were selected for their variation in overall Asteraceae composition. For each individual bee, we assessed C. bombi hindgut pathogen load via confocal microscopy, finding high levels of variation in infection status. We have submitted our samples for whole-genome sequencing and will assign sibship identities using COLONY (ver. 2.0.7.1) and assess apparent survival (i.e., lineage recapture) probability using a Cormack-Jolly-Seber mark-recapture model. Based on past work in our system, we expect that sites with high Asteraceae will contain workers with lower pathogen intensity/prevalence, which will predict higher recapture probability between colony cycles. Our results have vital implications for elucidating the drivers of bumblebee population persistence and evaluating a simple implementable conservation strategy to reduce harm from gut pathogens.