Night-Flying Moths
AS anyone who has ever passed a summer evening on a country porch will attest, moths are a highly varied group. The order Lepidoptera, besides butterflies, includes over 10,000 primarily nocturnal species of moths in North America and Mexico alone. Despit
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s anyone who has ever passed a summer evening on
a country porch will attest, moths are a highly varied group. The order Lepidoptera, besides butterflies, includes over 10,000 primarily nocturnal species of moths in North America and Mexico alone. Despite this great variety, a little over half of the 50 existing publications on moth thermoregulation concern just one family, the Sphingidae (commonly called "sphinx" or "hawk moths"), and 10 of these papers are on a single species, the common tobacco hornworm moth, Manduca sexta (formerly Protoparce). At a weight of 2 to 3 grams, M. sexta is one of the relatively large sphingids, a distinct advantage for a biologist seeking information on the physiology of body-temperature regulation of an insect. Most sphinx moths are so large, in fact, that they superficially resemble hummingbirds (Fig. 1.1). Roger Tory Peterson even depicts one alongside an Anna's hummingbird in the 1990 edition of his Field Guide to Western Birds. The smallest hummingbirds weigh near 3 grams, whereas sphinx moths may range in mass from a little under 300 milligrams to over 6 grams. And these generally nocturnal (some also fly in the daytime) moths are very rapid and adroit flyers that hover, as hummingbirds do, in front of flowers and sip nectar, although some species do not feed at all, relying instead on energy reserves accumulated during the larval stage. Sphingids are of particular interest to students of insect thermoregulation and energetics because of their historical importance. They were the first insects from which individual measurements of body temperature were taken; it was from them
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B. Heinrich, The Hot-Blooded Insects © Bernd Heinrich 1993
Fig. 1.1
"Hummingbird" moth, Hemaris sp., sipping nectar from a flower. Unlike most sphinx moths, Hemaris is diurnal, and unlike many it uses its first pair of legs for partial support while hovering.
we learned that insects were not necessarily all poikilothermic. Furthermore, they were the subject of stark controversies on the mechanism of insect thermoregulation, controversies that eventually stimulated productive research and sharpened our focus. More is known about thermoregulation in moths than in any other group of insects, except possibly bees, and they are now a model of many of the principles and mechanisms of insect thermoregulation in general. For these reasons I have chosen to examine them in detail both to illustrate general principles of thermoregulation in insects and to provide a historical perspective of how the insights were derived.
The Physiology of Pre-Flight Warm-Up The first person to measure the temperature of individual insects was the noted geologist Johann F. Hausmann, who in 1803 (quoted in Porfirij Bachmetjew, 1899) reported an increase of 2 ° C in the air temperature in a small vial containing a Sphinx convolvuli. Still using a mercury thermometer, but laying it against the insect directly, George Newport (1837) of the Entomological Society of London and the Royal College of Surgeons published temp
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