A new study reveals that intense summer heat in Arizona disrupts honey bees' ability to regulate hive temperatures, leading to population declines in smaller colonies. Researchers observed significant temperature fluctuations inside hives during prolonged heat waves exceeding 40°C. As climate change intensifies such events, the findings highlight risks to bees and their vital pollination role.
Honey bees are renowned for maintaining precise hive temperatures, but extreme heat can push this system beyond its limits. In a study published in Ecological and Evolutionary Physiology, scientists tracked nine colonies over three months in Arizona, where air temperatures often surpassed 40°C (104°F). The research, titled "Negative Effects of Excessive Heat on Colony Thermoregulation and Population Dynamics in Honey Bees," was led by authors including Jun Chen, Adrian Fisher II, Gloria DeGrandi-Hoffman, and Jon F. Harrison.
While colonies kept average brood temperatures at the optimal 34-36°C for development, daily fluctuations proved harmful. In the brood's center, developing bees endured about 1.7 hours below and 1.6 hours above this range each day. Conditions worsened at the edges, with nearly eight hours outside the safe window, exposing young bees to stress that could impair growth.
These swings correlated with population drops, particularly in colonies facing the highest peaks and variations. As the authors noted, "excessive heat, with maximal temperatures exceeding 40°C, can reduce colony populations by impairing the thermoregulation of brood or by exposing adults to temperatures that shorten their lifespans."
Larger colonies fared better, limiting edge fluctuations to around 6°C daily compared to 11°C in the smallest hives, thanks to more workers aiding cooling. The team emphasized that while bees use evaporative cooling, high humidity could hinder it further.
Looking ahead, the study warns of broader threats. Global temperatures may rise 2.7°C by century's end, or up to 4°C in high-emission scenarios, making heat waves more frequent. For beekeepers, this underscores the need for shade, supplemental water, improved insulation, and quality forage to bolster resilience and safeguard pollination-dependent agriculture.
