Abstract: Aphids are important pests of greenhouse vegetables, and chemical pesticides are widely used to control them. Release of ladybugs for the control of Myzus persicae can reduce the use of chemical pesticides, but high temperatures in the greenhouse may backfire the ladybugs performance. In this study, the survival rate and fecundity of two species ladybugs exposed to high temperature treatment were measured together with their control of M. persicae on pepper plants in greenhouses. The results showed that Coccinella septempunctata was able to reproduce normally at a variable temperature of 25℃ /37℃, but failed to reproduce at a constant temperature of 37 ℃, whereas Hippodamia variegata was able to reproduce normally at both a constant temperature of 37 ℃ and a variable temperature of 25℃ /37℃ . The occurrence of M. persicae on pepper plants increased since the beginning of June, peaked in late July, and then gradually decreased. The results of field experiments showed: eggs of C. septempunctata pretreated at variable temperature of 25/37 ℃ hatched at 46.8% in contrast to 88.3% at 25 ℃, which afforded a 88.5% control of M. persicae on pepper plants in contrast to 69.0% at 25 ℃ at 30 days post release of the eggs. Eggs of H. Variegata pretreated at variable temperature of 25℃ /37℃ and constant temperature of 37 ℃ hatched at 85.3% and 43.03%, respectively, in contrast to 79.1% at 25 ℃, which afforded 97.8% and 77.6% control of M. persicae on pepper plants, respectively, in contrast to 96.9% at 25 ℃ at 30 days post release of the eggs. This study shows that both species of ladybugs have to ability to adapt to and reproduce at high temperature of 37 ℃, and can be used in the control of M. persicae on pepper plants in greenhouses, although H. Variegata is a better choice than C. septempunctata.

Key words: Coccinella septempunctata, Hippodamia variegata, Myzus persicae, high temperature, biological control