EFFECTS OF AMBIENT OXYGEN-TENSION ON FLIGHT PERFORMANCE, METABOLISM, AND WATER-LOSS OF THE HONEYBEE

Although the metabolic rate of resting insects is relatively insensiti ve to atmospheric O-2 tensions, metabolic rates during flight increase by 20- to 100-fold above resting levels. In this study we test whethe r O-2 delivery limits metabolic rate during unladen hovering flight of the honeybee, Apis mellifera. Below 10 kPa PO2, wing-stroke frequency decreased, and at 5 kPa, bees could not fly. However, for PO2's rangi ng from 39 to 10 kPa, metabolic rate and wing-stroke frequency were un affected by PO2. Evaporative water loss rates increased by 40% at the lowest O-2 tensions, which suggests that flying honeybees compensated for decreasing ambient PO2 by modulating convective ventilatory flow. Under normal sea-level conditions, O-2 delivery does not limit flight metabolic rate in unladen, hovering honeybees and does not limit maxim al metabolic rate. At altitudes above 3,000 m, the convective componen t of O-2 delivery may, however, limit flight metabolic rate and flight capacity in honeybees.