Effect of Variable Temperature Environments on Egg Development of Three Species of Fruit Flies1

Abstract

Eggs of the oriental fruit fly, Dacus dorsalis Hendel, the melon fly, Dacus cucurbitae Coq., and the Mediterranean fruit fly, Ceratitis capitata (Wied.) were incubated under variable temperatures in automatically controlled, air-conditioned bioclimatic chambers. Idealized temperature patterns, with fixed periodicities and diurnal ranges, and natural temperature patterns, characteristic of many United States localities, were studied; the results of both types of thermal environments, which were closely alike, were compared with constant temperature results previously reported. Only at medial thermal levels (65°–85° F.) do egg development rates under regularly fluctuating temperatures agree closely with those at constant temperatures; at these levels, differences in the diurnal temperature range cause little or no change in rates. Below this medial zone, under variable temperatures there is an acceleration, and in the upper thermal levels a deceleration of development relative to that resulting from constant-temperature exposures, and the greater the diurnal variation, the greater are these effects. Exposures at the lower levels temperatures near or even below the constant temperature threshhold; in several cases completed development occurred after exposure to mean temperatures several degrees below that threshhold. Mean temperatures at high-level exposures never exceeded the constant-temperature upper developmental limit. Swiftest egg development under fluctuating temperature conditions occurred at mean temperatures 5 to 10 degrees below the temperature for most rapid growth under constant conditions; this maximum development rate was somewhat less under fluctuating conditions than when temperatures were held constant. When developmental rates for the egg stage of these flies are plotted against means of the fluctuating temperatures encountered during exposure, the resulting curves, though exhibiting some slight sigmoidal character at the extremities, approach rather closely a rectilinear relation. This is in contrast to the much more pronounced sigmoidal relationship of the corresponding curves noted in constant temperature studies.