Effect Of Survival And Development Of Propylaea Japonica(Coleoptera: Coccinellidae)Exposed To High Temperature Stress

Propylaea japonica?Thunberg??Coleoptera:Coccinellidae?is well known as a good biological control agent for aphids and soft-bodied insects in arid and semi-arid area in China.Extreme high temperatures in summer become more universal.How such events at different life stages affect fitness and performance remain unclear in most biological control agents.In this study,the effects of heat stress?35,37,39,41 and 43°C?and exposure duration?1,2,4and 6 h?on survival of egg,larval,pupal and adult stages of P.japonica were studied.On the other hand,the heat stress on the longevity and reproduction of adult stage,and egg hatch,larval development and sex ratio of F₁ progeny of P.japonica were determined.The main conclusions are as follows:The results revealed that there was no observed mortality at any developmental stages of P.japonica at 35 and 37°C for 6 h.According to the survivorship curve of egg,only temperature43°C?the highest temperature?could significantly affect egg of P.japonica.Survivorship of all four larval stages indicate that the first instar larvae are the most susceptible to high temperature but the thermotolerance of larval stage will be increased in older stage.The results of this experiment suggest that egg is most tolerant to high temperature,followed by the older larvae,pupae,and adults,respectively.The pre-oviposition period and fecundity among four treatment combinations in stressed and control adult stage did not significantly differed.The oviposition period was significantly decreased.Total developmental duration of F₁ progeny of P.japonica did not differ greatly,even though developmental duration of first instar female larva exhibited significant difference.F₁ progeny from the couples of stressed female and control male showed the highest sex ratio of male to total adults.Overall,extreme high temperature in summer has become more frequent in recent years in many regions around the world.Effects of heat stress on predatory ladybeetles depend on the high temperature,exposure duration and developmental stages.Our results highlight the importance of understanding how hot days affect fitness and performance of P.japonica with complex stage structure when forecasting population dynamics in the future.