High Temperature Adaptation Of The Beet Armyworm,Spodoptera Exigua(Lepidoptera:Noctuidae)

The beet armyworm,Spodoptera exigua(Hübner)(Lepidoptera: Noctuidae)is an important notorious agricultural pest worldwide.This pest has a wide range of host species,has seriously damaged most of the crop-producing areas of China and caused serious economic losses.In recent years,global warming and extreme heat events have resulted in frequent outbreaks of S.exigua in China.In the present study,the biological characteristics of S.exigua at constant temperature and short-term high temperature stresses were studied systematically by using the theory of high temperature biology and population ecology.Meanwhile,the response and adaptation mechanisms of S.exigua to high-temperature stresses were analysed from the perspectives of antioxidant response,heat shock proteins gene expression and variation in the structure of the gut bacterial community.The main findings are as follows:1.In the range of 24～32 °C,the developmental time of eggs,larvae and pupae was shortened,the adult longevity was declined and the number of eggs per female increased with increasing temperature;the suitable temperature range for development and reproduction of S.exigua was 26～30 °C.2.Short-term heat shock during the egg stage reduced hatching rate and prolonged the developmental time,shortened the larval developmental time and female adult longevity,while improved fecundity.Short-term heat shock during the early instar larvae decreased the survival of larvae and prolonged larval development time,improved fecundity.Short-term heat shock during the late instar larvae shortened the larval developmental time,prolonged the pupal developmental time,shortened adult longevity and reduced fecundity.3.After five generations treatment,the survival rate of total larvae increased to the control leve,while the survival rate of the early larvae,pupation rate,fecundity and adult longevity decreased significantly.The activities of the three enzymes in the first generation showed an increase followed by a decrease with the increase of temperature,while there was no significant difference after five generations treatment.After five generations treatment,the expression levels of Hsp70 and Hsp90 genes did not differ from the control at 38 °C,and the expression levels at 41 °C and 44 °C were significantly lower than those of the control.4.The richness and diversity of gut bacteria decreased after high-temperature stress were lower than the control,but the community composition was similar to that of the control.In contrast,the richness and diversity of gut bacteria increased after low-temperature stress,and the community composition was different from the control.Both high-and low-temperature stress could change the composition of intestinal microbes.The gut bacterial community of S.exigua gradually stabilised in five generations under high-temperature stress.The diversity of gut bacterial community decreased in first generation,and the bacterial community structure and composition were similar to the control.The bacterial community structure and composition from second generation to fifth generation were similar.After high-temperature stress,all functions in the larvae of the first generation decreased,while the second generation to the fifth generation were increased after stress.