Picky eaters: Foraging specialization in a superorganism is affected by individual age and colony senescence; a look at bumble bees (Bombus impatiens)

The evolution of behavioral specialization is an important feature of cooperative units ranging from cells within a multicellular organism to superorganisms such as social insects. By studying primitively eusocial species such as bumble bees, we can learn more about how such specialization evolved and how it differs between species with limited (annual) colony lifespan such as bumble bees and those with potentially immortal (perennial) colony lifespan such as honey bees. We therefore studied how foraging preferences (pollen vs. nectar) changed in bumble bee, Bombus impatiens, foragers over individual and colony lifespan. Bees born in young colonies tended to forage for nectar rather than pollen. However, as colonies aged, newly born bees tended to forage mainly for pollen. Moreover, bees that began foraging early in their lives were more likely to forage for nectar than bees that began foraging when they were older. Bees born at the end of a colony’s lifespan tended to be less motivated and made fewer nectar foraging trips per day. Overall, 46% of foragers were specialized and spent 90% of their foraging effort on only nectar or pollen. Currently, we are determining the extent of behavioral flexibility by removing pollen specialists. We hypothesize that colonies can flexibly adapt by individuals switching their foraging preferences, changes that are also affected by colony senescence.