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A laboratory cotton leaf disc experiment was conducted to study the effects of different temperature (32, 34, 36, 38, and 40 degrees C) and density (5, 25, 50, and 75 individuals per dish) on the mortality and reproduction of Aphis gossypii. With the increase of temperature, density, and culture duration, the cumulative mortality of A. gossypii presented an increasing trend. The parameters estimated by complementary log-log (CLL) model showed that the beta value decreased with the increase of density, indicating that the effects of temperature weakened with increasing density. The gamma value, a parameter for the time effect of temperature, changed with culture duration, indicating that the morality of A. gossypii was co-affected by the temperature and culture duration. The two-way ANOVA analysis of variance showed that temperature and density had significant effects on the fecundity of A. gossypii, and there existed interactive effect. At 32-36 degrees C, the reproduction rate of A. gossypii decreased with the increase of density, but at 40 degrees C, no significant difference was observed in the reproduction rate under different densities, suggesting that the density effect was weakened with increasing temperature, i. e., the contribution of temperature and density to the survival and reproduction of individual varied with the ranges of the temperature and density. This study could provide reference for the monitoring and forecasting of A. gossypii population and for the improvement of pests control.

Aphis gossypii and Acyrthosiphon gossypii are the coexisting species on cotton plant, with their abundance differed within and among years. To explore whether the abundance difference was related to the different responses of the two aphid species to high temperature, a laboratory experiment was conducted to assess the mortality and reproduction of the two aphid species at high temperatures 32, 34, 36 and 38 degrees C. With the increasing temperature and prolonged exposure period, the cumulative mortality of the two aphid species increased, and Acyrthosiphon gossypii had a higher cumulative mortality than Aphis gossypii. The daily mortality of the aphids could be well simulated by complementary log-log (CLL) model. The median lethal temperature of the two aphid species estimated by CLL model decreased with prolonged exposure period. Under the same exposure period, the median lethal temperature of Aphis gossypii was higher than that of Acyrthosiphon gossypii. Within the range of 32-38 degrees C, the reproduction rate of the two aphid species decreased with increasing temperature, but Aphis gossypii had a significantly higher reproduction rate than Acyrthosiphon gossypii, indicating that at the temperature higher than 32 degrees C, Aphis gossypi had higher tolerance against high temperature than Acyrthosiphon gossypii, and consequently, had more competitive advantage under global warming.