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

Simple Summary As poikilotherms, insects are sensitive to ambient environmental conditions; therefore, it is important to gauge how heat stress affects their survival and fitness. The ladybeetles Hippodamia variegata (Goeze) and Propylaea quatuordecimpunctata (Linnaeus) are key natural enemies within cotton fields in Xinjiang Province, China. This study investigated the effects of different temperatures (i.e., 32, 35, and 38 degrees C) on the survival, reproduction, predation, and antioxidant capacity of adult ladybugs. Laboratory assays showed that elevated temperatures (i.e., 35 and 38 degrees C) impacted P. quatuordecimpunctata survival and reproduction to a greater extent than that of H. variegata. At all experimental temperatures, H. variegata's predation rate on aphid prey surpassed that of P. quatuordecimpunctata. Yet, prey consumption rates of H. variegata were highest at 35 degrees C, while those of P. quatuordecimpunctata gradually decreased with higher temperatures. Lastly, superoxide dismutase (SOD), catalase (CAT), peroxidases (POD), glutathione-s-transferases (GSTs), total antioxidant capacity (T-AOC), and protein content in both ladybugs were significantly affected by ambient temperature. By assessing the thermal biology of individual ladybug species, laboratory assays can thus explain their spatiotemporal distribution and inform strategies to enhance biological control under conditions of global warming or extreme weather events. 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 degrees C. The (negative) impacts of elevated temperatures (i.e., 35 and 38 degrees 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.

Automated summary

This study investigated the effects of different temperatures on the survival, reproduction, predation, and antioxidant capacity of two ladybug species. The results showed that elevated temperatures had a greater impact on one species, while the other species had a higher predation rate on aphid prey. In addition, the antioxidant capacity of both species was significantly affected by ambient temperature.