Summer diapause in the cotton bollworm, Helicoverpa armigera (Hübner), is prolongation of the pupal stage, particularly in males, induced by high temperatures. The effects of exposing a parental generation to temperatures of 33 to 39°C on the development, survivorship, longevity and fecundity of their offspring were determined in the laboratory. Three groups of offspring were examined: A, the progeny of control female moths reared as larvae at 27°C mated to male moths that had undergone summer diapause when exposed to high temperature; B, the progeny of control female moths mated to males that had not undergone summer diapause after exposure to high temperature; C, the progeny of control females mated to control males reared at 27°C. The developmental times of the immature stages were significantly different between groups. The survival rate in the immature stages varied significantly from 69.8% (Group C) to 34.7% (Group B). The average number of eggs produced per female and the longevity of females and males were not significantly different. The indices of population increase of Groups C, A and B were 286.2, 256.8 and 145.0, respectively. These results indicate that Group A offspring had physiological advantages, such as survival and population increase, compared to Group B offspring. The adaptive significance of summer diapause in the cotton bollworm is discussed in relation to the performance of offspring.