Honeybee flight metabolic rate: does it depend upon air temperature?

Area of Science:

• Insect physiology
• Thermoregulation
• Animal behavior

Background:

• Honeybee (Apis mellifera) thermoregulation during flight is debated.
• Understanding flight energetics and heat production is crucial for insect physiology.

Purpose of the Study:

• Investigate the impact of ambient air temperature on honeybee flight metabolic rate.
• Examine thermoregulatory responses including water loss, wingbeat frequency, and body temperatures.
• Analyze behavioral adjustments in response to varying temperatures.

Main Methods:

• Honeybees were studied in outdoor transparent containment to measure flight metabolic rate, water loss, wingbeat frequency, and body temperatures.
• Voluntary, self-sustaining flight was observed, alongside flight under agitation.
• Data analysis correlated these parameters with ambient air temperature.

Main Results:

• Flight metabolic rate remained constant between 19-37°C during voluntary flight.
• Thorax temperature showed minimal variation (slope of 0.18).
• Evaporative heat loss significantly increased with air temperature, while head and abdomen temperatures decreased.
• Wingbeat frequency increased, and metabolic cost per wingbeat decreased with rising air temperature.
• Bees flew less as temperatures rose, and metabolic rate decreased with temperature when flight was not sustained.
• Agitated flight showed an inverse metabolic rate-temperature relationship, unlike voluntary flight.

Conclusions:

• Honeybee flight metabolism is largely independent of air temperature during voluntary flight within a specific range.
• Thermoregulation is achieved through increased evaporative cooling at higher temperatures.
• Behavioral adjustments, like reduced flight time, are critical for thermoregulation in warmer conditions.
• Existing hypotheses on metabolic rate-temperature slopes are supported for voluntary flight but not under agitation.