INDUCTION OF IMMUNE DEFENSE IN APIS MELLIFERA AND BOMBUS IMPATIENS

Background: Global bee populations are declining in devastating numbers, as bees are critical pollinators, this loss threatens the global food supply and biodiversity. Methods: We hypothesized that chronic, sub-lethal immune stimulation represents an energetic tax on the individual bee and negatively impacts colony fitness when compounded over thousands of members and multiple generations. Immune defense induction in Apis mellifera, the European honeybee, and Bombus impatiens, a bumblebee species native to North America, was examined. When bees are exposed to a pathogen the initial immune system response includes the initiation of expression of antimicrobial peptides. Four principal bee antimicrobial peptides (AMPs), Defensin 1, Abidaecin, Hymenoptaecin and Apidaecin are well-conserved between Apis and Bombus species. Fitness costs associated with immune defense are measured by assessing forager performance on navigational challenges that model tasks critical to colony health. To induce immune defense, forager bees are injected with LPS and peptidoglycans, Gram (-) and (+) moieties and B-1, 3 Glucans, a component of fungal cells. AMP expression is assessed with quantitative PCR. To discern whether immune response varies between species, parallel analysis is performed on two pollinator species, Apis mellifera and Bombus impatiens. Results: Bumblebee AMP expression peaks at 12 and 24 hours post injection of immune stimulants. Interestingly, bumblebees injected with LPS exhibited drastically reduced foraging behaviors, but this effect was not observed in bees injected with B-1, 3 Glucans. Comparative analysis on honeybees is pending. Conclusion: The data collected is increasing our knowledge of immune strategies in these critically important bee species. Reduced foraging in bumblebees indicates that this species incurs a fitness cost upon immune stimulation. We expect that honeybees will similarly respond to immune stimulation by demonstrating a decreased aptitude for foraging.