Temperature Regulation Of Honey Bees (Apis Mellifera) Foraging In The Sonoran Desert

ABSTRACT A heat budget for foraging honey bees (Apis mellifera L.) indicated that at 30-35 °C all bees are in positive heat balance during flight. Observations of honey bees returning to their hives at high ambient temperatures support the conjecture that honey bees regulate head and thorax temperatures at high Ta by regurgitating droplets of honey stomach contents which are then evaporated. The proportion of returning bees with a droplet on the tongue increased with increasing shade temperature (Ts), from essentially no bees at 20°C to 40% of returning bees at 40°C. Pollen foragers carry relatively little fluid during the hottest periods, and pollen foraging decreased at high ambient temperatures. Thoracic temperatures of pollen collectors are significantly higher than thoracic temperatures of water and nectar gatherers at 40°C (46·13 vs 44°C). Additionally, water and nectar foragers with extruded droplets have slightly cooler heads and thoraces (38·94 and 43·22°C) than bees not extruding droplets (40·28 and 44·18°C). Wingloading and thoracic temperatures of bees are inversely correlated at high ambient temperatures (35 °C) and this is probably caused by a higher propensity of heavier bees to extrude fluid, thus reducing thoracic temperature.