Factors affecting the reproductive health of honey bee (Apis mellifera) drones—a review

Abstract

In the honey bee, Apis mellifera , colonies are composed of one queen, thousands of female workers, and a few thousand seasonal males (drones) that are reared only during the reproductive season when colony resources are plentiful. Despite their transient presence in the hive, drones have the important function of mating with virgin queens, transferring their colony's genes to their mates for the production of fertilized, worker-destined eggs. Therefore, factors affecting drone health and reproductive competency may directly affect queen fitness and longevity, having great implications at the colony level. Several environmental and in-hive conditions can affect the quality and viability of drones in general and their sperm in particular. Here we review the extant studies that describe how environmental factors including nutrition, temperature, season, and age may influence drone reproductive health. We also review studies that describe other factors, such as pesticide exposure during and after development, that may also influence drone reproductive quality. Given that sperm development in drones is completed during pupation prior to adult emergence, particular attention needs to be paid to these factors during drone development, not just during adulthood. The present review showcases a growing body of evidence indicating that drones are very sensitive to environmental fluctuations and that these factors cause drones to underperform, potentially compromising the reproductive health of their queen mates, as well as the overall fitness of their colony.

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

“…An additional 13 publications providing data from bumble bee microcolony [ 14 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], queenright colony [ 30 , 31 ] studies and relevant testing guidelines [ 32 , 33 ] were found by reviewing the reference section of [ 34 ]. Four publications providing background on honey bee males were also included in this review [ 20 , 35 , 36 , 37 ]. Publications discussed in this review are specifically focused on male bumble bee biology, their role within the nest, sensitivity to toxicants, immunity, mating behavior, reproductive measures, and their combined impact on queen success and colony viability ( Table 1 ).…”

“…Currently, there are no accepted methods for assessing chronic toxicity or colony-level effects in bumble bees of any caste. While Apis bee researchers are beginning to recognize the importance of drones to colony reproductive health [37], bumble bee drones contribute far more to colony success than the act of insemination. Bumble bee drones are dynamic partners in the colony, making contributions to the genetic composition of the colony, maintaining brood nest temperature and, in stark contrast to honey bee drones, Bombus drones contribute directly to queen overwintering survival and by extension foundress activity.…”

Honey Bee Queens and Virus Infections

“…The queen is a critical member of the honey bee colony, and her primary roles are prolific egg production and the release of pheromones that maintain social cohesion [8][9][10]. In addition to the queen's genetic make-up, queen quality-including health status and reproductive vigor-is a consequence of the nurse bees' care during development of the queen larva, the health and fertility of the~15 drones with which she mates, and the care she receives from worker bees in her colony after mating [11][12][13][14][15][16][17][18][19]. Simultaneously, queen health and reproductive capacity have direct impacts on the health, well-being, and vigor of the colony she is heading [8,20,21].…”

Sperm Quality Assessment in Honey Bee Drones

“…This reduction naturally occurs during the second stage of eversion of the endophallus and during the injection of semen into the lateral oviducts of the queen, and has been attributed to increased pressure on the sperm during these stages. The sperm viability may also vary according to drone age, nutrition, management practices, environmental factors and exposure to insecticides and miticides [105].…”