Morphological and Reproductive Plasticity and Fluctuating Asymmetry of Myzus persicae (Sulzer) (Hemiptera: Aphididae) Under Different Temperatures

Four clones of the aphid Myzus persicae (Sulzer) were used to assess the magnitude of their responses to seven different temperatures (15.0, 17.5, 20.0, 22.5, 25.0, 27.5 and 30.0 degree C). A multivariate index of size was obtained using five morphological characteristics simplified by PCA. Among these characteristics, four were measured bilaterally both sides in order to evaluate the fluctuating asymmetry (FA). Fertility was estimated according to the number of nymphs in the reproductive female apparatus. The variability attributed to the environmental and genetic components was estimated using a genetic quantitative model. A large part of the total variability found for size distribution was attributed to differences in temperature (environmental component), but genetic components of variation were also detected. The plastic potential was considered adaptive, since it increases clone survival in unstable environments and allows new habitat exploitation. However, 30 degree C temperature did not permit clone development and survival. Lower variability in one morphological character, the rostrum, in comparison with the other traits may be the result of a stabilizing selection, in relation to its adaptive value to obtain food. The aphids presented FA in some of the measured characteristics. However, no linear relation was detected for the levels of FA and temperature values and no general pattern of variability was found. The data corroborate the hypothesis that size is more effectively affected than FA by external influences, and consequently, is a much more efficient indicator of environmental stress.