Impact of Heat Stress on the Predatory Ladybugs Hippodamia variegata and Propylaea quatuordecimpunctata

Abstract

In cotton-growing regions of northwestern China, Hippodamia variegata (Goeze) and Propylaea quatuordecimpunctata (Linnaeus) (Coleoptera: Coccinellidae) are key natural enemies of hemipteran pests. As only H. variegata can be encountered in hot, arid production areas, the thermal responses and climatic adaptability of both species likely differ substantially. In this study, we assessed the survival, longevity, fecundity, prey consumption rate, and antioxidant capacity of both species under laboratory conditions at 32–38 °C. The (negative) impacts of elevated temperatures (i.e., 35 and 38 °C) on adult survival and reproduction were more pronounced for P. quatuordecimpunctata than for H. variegata. Similarly, high temperatures exhibited the strongest negative impacts on the prey consumption rates of P. quatuordecimpunctata. At elevated temperatures, superoxide dismutase and catalase activity increased, while glutathione-S-transferases activity decreased for both species. However, for P. quatuordecimpunctata, peroxidase activity and total antioxidant capacity progressively declined. Antioxidant responses thus constitute a key physiological adaptation of ladybugs to heat stress, reflecting a superior thermal tolerance of H. variegata. Our work emphasizes how laboratory assays can explain spatiotemporal distribution patterns of individual ladybugs and inform strategies to bolster their ensuing biological control under conditions of global warming or extreme weather events.