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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 honey bee (Apis mellifera L.) contributes ∼$17 billion annually to the United States economy, primarily by pollinating major agricultural crops including almond, which is completely dependent on honey bee pollination for nut set. Almond growers face constant challenges to crop productivity owing to pests and pathogens, which are often controlled with a multitude of agrochemicals. For example, fungicides are often applied in combination with other products to control fungal pathogens during almond bloom. However, the effects of fungicides on honey bee health have been so far understudied. To assess the effects of some of the top fungicides used during the 2012 California almond bloom on honey bee forager mortality, we collected foragers from a local apiary and exposed them to fungicides (alone and in various combinations) at the label dose, or at doses ranging from 0.25 to 2 times the label dose rate. These fungicides were Iprodione 2SE Select, Pristine, and Quadris. We utilized a wind tunnel and atomizer set up with a wind speed of 2.9 m/s to simulate field-relevant exposure of honey bees to these agrochemicals during aerial application in almond fields. Groups of 40-50 foragers exposed to either untreated controls or fungicide-laden treatments were monitored daily over a 10-d period. Our results showed a significant decrease in forager survival resulting from exposure to simulated tank mixes of Iprodione 2SE Select, as well as synergistic detrimental effects of Iprodione 2SE Select in combination with Pristine and Quadris on forager survival.

Honey bee (Apis mellifera) colonies invest a substantial amount of colony resources in the production of drones during the reproductive season to enable mating with virgin queens from nearby colonies. Recent studies have shown significant differences in the production of sperm cells that are viable (i.e., sperm viability) and can fertilize an ovule among sexually mature drones that are exposed to different environmental conditions during development or as adults. In particular, sperm viability may be negatively affected during drone development from exposure to pesticides in contaminated beeswax. To assess whether sperm viability is negatively affected during drone development from exposure to beeswax contaminated with in-hive pesticides, we compared the viability of sperm collected from drones reared in pesticide-free beeswax with that of drones reared in beeswax contaminated with field-relevant concentrations of the pesticides most commonly found in wax from commercial beekeeping operations in the United States. These pesticides include the miticides fluvalinate, coumaphos and amitraz, and the agro-chemicals chlorothalonil and chlorpyrifos. Sperm from drones collected at 10 and 18 days post emergence were classified as viable or non-viable to calculate sperm viability. For all pesticide treatment groups, drones that were reared in pesticide-laden beeswax had lower sperm viability compared to those reared in pesticide-free beeswax. This difference was especially pronounced among drones reared in miticide-laden wax. Our results reinforce the notion that pesticide contamination of beeswax negatively affects the reproductive quality of drones, which can affect the queens they mate with, ultimately compromising colony health.

The honey bee (Apis mellifera L. (Hymenoptera: Apidae)) contributes an essential role in the U.S. economy by pollinating major agricultural crops including almond, which depends entirely on honey bee pollination for successful nut set. Almond orchards are often treated with pesticides to control a variety of pests and pathogens, particularly during bloom. While the effects to honey bee health of some insecticides, particularly neonicotinoids, have received attention recently, the impact of other types of insecticides on honey bee health is less clear. In this study, we examined the effects to honey bee forager survival of three non-neonicotinoid pesticides widely used during the 2014 California almond bloom. We collected foragers from a local apiary and exposed them to three pesticides at the label dose, or at doses ranging from 0.5 to 3 times the label dose rate. The selected pesticides included the insect growth regulators methoxyfenozide and pyriproxyfen, and the acaricide bifenazate. We simulated field exposure of honey bees to these pesticides during aerial application in almond orchards by using a wind tunnel and atomizer set up with a wind speed of 2.9 m/s. Experimental groups consisting of 30-40 foragers each were exposed to either untreated controls or pesticide-laden treatments and were monitored every 24 hr over a 10-d period. Our results revealed a significant negative effect of all pesticides tested on forager survival. Therefore, we suggest increased caution in the application of these pesticides in almond orchards or any agricultural crop during bloom to avoid colony health problems.

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