Cryobiology of the Face Fly and House Fly (Diptera: Muscidae)

Face flies, Musca autumnalis De Geer, have a circumpolar distribution and overwinter as adults in reproductive diapause. House flies, Musca domestica L., have a cosmopolitan distribution and overwinter in northern latitudes in animal confinement quarters. We compared supercooling points with low temperature tolerances, as measured by bioassays, in all developmental stages of both species. There was no correlation between supercooling points and the ability to survive subzero temperatures. Rapid cold hardening was induced in adults of both species by a 2-h acclimation period at 0 degrees C. Hemolymph melting points were measured osmometrically in diapausing and reproductive face flies. Freezing point depressions differed between diapausing and reproductive flies and between reproductive flies given a 2-h pre-exposure to 0 degrees C and unexposed flies. Our data suggest that a -8 to 8 degrees C range with a mean close to 0 degrees C is necessary for successful face fly overwintering. House fly overwintering sites must offer microhabitats that remain above -5 degrees C with sufficient time above 10 degrees C to allow larval, pupal, and ovarian development.