Larval ejection behavior in native bumble bee colonies

Bumble bees are social insects that are key native pollinators in the US. Their colonies require a continuous supply of high quality pollen and nectar to fulfill the dietary needs of developing larvae. When food resources are scarce, workers are known to eject larvae, though qualitative and quantitative information about larval ejection behavior are lacking. The objective of this study was to determine the impact of food resources, both pollen and nectar, and their abundance, on the larval ejection behavior in colonies of the native bumble bee, Bombus vosnesenskii. Lab-reared colonies, initiated by the collection of wild queens, were assigned in separate experiments to four pollen and nectar treatments (none, low, standard, high) using a randomized block design with five replications. Larval ejection occurred in all pollen and nectar treatments. An analysis of variance test indicated that there was no significant difference in larval ejection across all treatments in both pollen (P=0.69) and nectar (P=0.85) experiments. However, overall larval mortality (larval ejection and dead larvae within the colony) was found to be significantly higher in colonies exposed to no pollen (P < 0.01) and no nectar (P < 0.01) compared to the other treatments. Implications of the responses of bumble bee colonies to limited food resources, and the critical need for adequate and continuous pollen and nectar resources for sustainability of pollination services in cropping systems and wild habitats will be discussed.