Vulnerability of honey bee queens to heat-induced loss of fertility

All species need to reproduce to maintain viable populations, but heat stress kills sperm cells across the animal kingdom and rising frequencies of heat waves are a threat to biodiversity. Honey bees (Apis mellifera) are globally distributed microlivestock; therefore, they could serve as environmental biomonitors for fertility losses. Here, we found that queens have two potential routes of temperature-stress exposure: within colonies and during routine shipping. Our data suggest that temperatures of 15-38 degrees C are safe for queens at a tolerance threshold of 11.5% loss of sperm viability, which is the viability difference associated with queen failure in the field. Heat shock activates expression of specific stress-response proteins in the spermatheca, which could serve as molecular biomarkers (indicators) for heat stress. This protein fingerprint may eventually enable surveys for the prevalence of heat-induced loss of sperm viability in diverse landscapes as part of a biomonitoring programme. Heat waves can pose a threat to biodiversity as heat stress kills sperm cells across the animal kingdom. Here, honey bee queens are found to be vulnerable to temperature changes and the specific stress-response proteins activated in the spermatheca are discussed as potential indicators of heat stress.