Effect of shipping boxes, attendant bees, and temperature on honey bee queen sperm quality (Apis mellifera)

Abstract

The fertility and fecundity of the queen are vital to the success of a honey bee colony (Apis mellifera L.). Young mated queens are shipped worldwide to meet the demand of the beekeeping industry. Since little is known about the conditions experienced by queens in transit from breeders to beekeepers and the importance of these conditions on the queens' reproductive potential, we conducted a two-part study. First, queen shipments from the USA and Canada to Canadian beekeepers were monitored to measure thermal conditions during shipment. A total of 39 shipments were followed in 2017 and 2018. Monitoring revealed variable temperatures during shipment, with occasional periods of lows (10-15°C) and highs (30-36°C). Second, young mated queens were placed in different shipping boxes with or without attendant bees and exposed to one of three temperatures (6°C, 26°C, and 40°C) for 2 h. We then compared the thermoregulation within shipping boxes, and the viability of sperm in each queen's spermatheca. Our results show that both low and high temperatures significantly decrease sperm viability, and that the addition of loose attendant bees within shipment boxes helps maintain the temperature at 26°C when exposed to low temperature and delays the temperature increase when temperatures are high. The study shows the potential to improve current honey bee shipping methods in order to mitigate variable conditions experienced by bees during transportation.

Queens, but not their stored sperm, are resilient to temperature stress

“…We and others have previously found that exposure to extreme temperatures signi cantly reduces viability of stored sperm [7][8][9], as well as drone ejaculates [8,20], but here we detected no effect of temperature on sperm viability (Fig. 1c).…”

“…As such, a queen's lifetime reproductive capacity is ultimately sperm-limited, and any decrease in the viability of her stored sperm results in a permanent change to her fecundity and longevity [1,6]. Previous research has shown that extreme temperatures (both hot and cold) can reduce viability of stored sperm, and temperature stress has been proposed as potential causal factor underlying queen failure in apiculture operations [7][8][9].…”

“…Queens are vulnerable to temperature stress during shipping and potentially inside small colonies during extreme weather events (i.e., heatwaves) [7][8][9]. Queen honey bees are routinely shipped both domestically and internationally to satisfy the seasonal needs of beekeepers.…”

“…In the United States, queens are mainly produced by a relatively small number of large-scale queen production operations in Hawaii, California, and the southeastern states for domestic distribution. Queens are typically shipped in small cages with poorly thermoregulated environments, leaving them vulnerable to perturbations in ambient temperatures [7][8][9].…”

“…However, this effect was apparently not linked to sperm viability, suggesting that temperature may impact other aspects of queen physiology. Worryingly, temperature stress events have been documented repeatedly during routine queen shipping [7][8][9]. While this is known to directly impact queen fertility via reductions in sperm viability, neither maternal effects on egg laying nor vertical impacts on her progeny have been investigated.…”