Development, survivorship and reproduction of Helicoverpa armigera (Lepidoptera: Noctuidae) under fluctuating temperatures

Laboratory studies were conducted to assess the effect of temperature on the survival, development, longevity and fecundity of Helicoverpa armigera (Lepidoptera: Noctuidae) at eight different fluctuating temperatures with an amplitude +/- 9 degrees C under constant photoperiodic conditions of 16: 8h (L:D). H. armigera achieved complete development from egg to adult emergence between mean 17.5 and 32.5 degrees C. At mean 35 degrees C, all newly hatched larvae died and at mean 15 degrees C entered diapause at pupal stage. The lower developmental thresholds of the immature stages were estimated by a linear model and ranged from 4.63 degrees C (pupal stage) to 7.69 degrees C (egg stage). The developmental thresholds estimated by a nonlinear model were slightly higher than those estimated by the linear model. Adult longevity and fecundity were reduced at mean fluctuating temperatures 17.5 and 32.5 degrees C, but tended to be independent of the pattern of temperature change at moderate temperatures. The maximum reproductive performance, 1130 eggs per female, was observed at mean 25 degrees C. The intrinsic rates of increase were positive, meaning that H. armigera could be expected to persist or increase in number between mean 17.5 and 32.5 degrees C, with the maximum value at mean 27.5 degrees C. H. armigera survives, develops and reproduces within a wide range of fluctuating temperatures, while it completes the above functions with different levels of success at different mean temperatures of diurnal variation. Comparison of our results with similar data from the literature involving constant conditions is discussed. This information will provide a better understanding of H. armigera phenology and population dynamics under natural conditions and is essential to understanding the ecological and evolutionary consequences of climate change on this important species.