> ... drones are surprisingly heat sensitive. When we exposed males to a temperature of 40°C for 24h, they all died (unpublished data). Furthermore, an exposure of males to 42 °C for 4h still resulted in substantial mortality of 77%. In these pilot experiments, all drones of the control group survived. 

> Consequently, we ended up exposing males in our formal experiment to rather moderate levels of heat (39 °C), which nevertheless resulted in a significant decrease in sperm viability. 

> There was also a strong effect of male age, a difference that was largely driven by the 10-day-old drones, which had significantly lower sperm viability than the 15- and 16-day-old drones, suggesting that sperm of fully mature drones is more robust to heat shock.

Stürup, Marlene, et al. "When every sperm counts: factors affecting male fertility in the honeybee Apis mellifera." Behavioral Ecology 24.5 (2013): 1192-1198.

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