The Importance of Males to Bumble Bee (Bombus Species) Nest Development and Colony Viability

SIMPLE SUMMARY: Populations of some bumble bee species have declined over the last decade. Recognizing the importance of bumble bees to agriculture and natural ecosystems, there has been an upwelling of research to better understand the underlying reasons for observed population declines. While most research has addressed the health of bumble bee females (i.e., workers and queens), males have been largely ignored. Here, we explore the available published literature on the role males play in improving queen health and reproductive fitness, as well as in overall nest success. We conclude that males serve a unique and important role in bumble bee colony success. ABSTRACT: Bumble bee population declines over the last decade have stimulated strong interest in determining causative factors and necessary conservation measures. Research attention has largely been directed toward bumble bee worker and queen health and their contributions to population stability, while male bees (i.e., drones) have typically been overlooked regarding their role in influencing colony fitness and longevity. In this review we assess existing literature on the diverse role of males within bumble bee nests and their importance to queen health and fitness, as well as to overall nest success. The implications of reproductive measures, including sperm transfer, mating behavior, mating plugs, and male immunity, among other topics, are examined. Overall, bumble bee males are found to drive colony function in a unique manner. Current knowledge gaps pertaining to the role of males are discussed. We highlight the importance of drones to queen success and fitness in many ways, and suggest future research exploring impacts of this often-neglected caste.