Effects of Constant and Fluctuating Temperatures on Developmental Rates and Demographic Statistics for the Corn Leaf Aphid (Homoptera: Aphididae)

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Abstract
Relationships between temperature and developmental rate of immature apterous and alate corn leaf aphids, Rhopalosiphum maidis (Fitch), were studied in the laboratory at constant and fluctuating temperatures. Estimates of lower (6.1°C) and upper (26.3°C) thresholds for development were determined from studies done at constant temperatures. Developmental rates were determined and demographic statistics estimated for cohorts of corn leaf aphids exposed to fluctuating temperature regimes that simulated average and extreme low and high temperature conditions during late spring in eastern South Dakota. For cohorts exposed to fluctuating temperatures, degree-day (DD) summations using lower and upper developmental thresholds were consistent with expected DD requirements derived from constant temperature studies of development. Demographic statistics expressed on a DD time scale differed among cohorts of apterous and alate corn leaf aphids exposed to identical temperature regimes. For each temperature regime, the intrinsic rate of increase of apterae exceeded that of alatae. However, temperature had a negligible effect on potential population growth rates of either morph. Stable in star distributions for apterous corn leaf aphid cohorts were only slightly affected by temperature; approximately 57, 19, 10, 6, and 8%of each cohort were first, second, third, and fourth instars and adults, respectively.