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Temperature Regulation in Bee- and Waspmimicking Syrphid Flies
1 Department of Biology, University of California, Riverside, CA 92521, USA
2 Department of Zoology, University of Vermont, Burlington, VT 05405, USA
Thoracic temperatures were measured in 12 syrphid species.
During field activity the flies maintained thoracic temperatures near 30°C by a combination of basking and endothermy. In the 10 species which were mimics of Hymenoptera, thoracic temperatures averaged a few degrees below those of their models.
All of the syrphids tested demonstrated a marked capacity for endothermic warm-up in the laboratory. Warm-up rates ranged from 1.2-5.5°C min-1. The maximum rate of warm-up increased in a linear fashion with body mass, with a slope of 4.3.
The flies sometimes sustained endothermy beyond the 2-5 min necessary for thoracic temperature to reach flight temperature. One individual maintained an average temperature excess of 13.4°C for more than 26 min.
Cooling rates were highly dependent on body mass and did not differ significantly between pubescent Bombus mimics and glabrous species. Removal of pile from the thorax of Bombus mimics increased their cooling rates by about 30%.
From the comparisons between wasp and bee mimics, we conclude that although the pubescence of Bombus-mimicking flies aids endothermy, it is not necessary to achieve it. Their pubescence has apparently evolved primarily to improve visual mimicry.
Key words: Diptera, Syrphidae, thermoregulation
Accepted on May 8, 1987
