Abstract
The spotted alfalfa aphid, Therioaphis maculata (Buckton), has been exposed to a series of rhythmically fluctuating temperature, humidity, and light patterns of 24-hour periodicities to evaluate the bioclimatic limits and optimal conditions for development, reproduction, and survival. Comparison of results has been made with similar data from the literature involving constant conditions. Fluctuating conditions are found to stimulate more rapid development of the aphid, to cause development to proceed to completion at lower temperatures, and to enhance greatly aphid fecundity and longevity as compared with effects of constant conditions. The temperature limits (means of the fluctuating conditions) to development are 6° C and 32.5° C, with optimum at 26-29° C. For reproduction the limits are the same, but the optimum (condition for maximum fecundity) is near 16° C. Survival is reduced only near 8° and 32° C. The intrinsic rate of population increase, computed from life table data, is used as a bioclimatic index reflecting the joint influence of the various physical conditions on development, reproduction, and survival. This index is positive (meaning the aphid could be expected to persist or increase in numbers) between 6° C and 33° C, with maximum value near 29° C.