Physiological And Biochemical Characteristics With Intestinal Microorganisms During Overwintering Of Dendroctonus Valens

Dendroctonus valens Le Conte is an important forestry quarantine pest in China.Its larva causes serious damage to the roots of pine trees,e.g.,Pinus tabulaeformis,P.armandii,and P.sylvestris.In recent years,its occurrence has gradually spread to the north,the area of occurrence has continued to expand,and the degree of harm has been increasing.Low temperature has a direct impact on the growth and development of insects and population spread.Cold tolerance is particularly important for population reproduction of D.valens.Adaptation to the low temperature environment in the north is very important for D.valens during overwintering.At present,there are few studies on the cold tolerance of D.valens.In this study,the cold tolerance,biochemical substances in the body,protective enzymes and community changes of intestinal fungi and bacteria were investigated using overwintering and non-overwintering larvae and adults of D.valens.The results were as follows:1?The supercooling point(SCP)and freezing point(FP)of overwintering larva and adult were clarified.The SCP of larva in wintering period is-18.34±0.26?,and the SCP adult is-18.59±0.63?.There is no significant difference of SCP between the larvae and adults.The FP of larva in wintering period is-10.17±0.36?,and the FP of adult is-15.90± 0.70?,and there is a significant difference of FP between the larvae and adults.2?The main cold-resistant substances in overwintering and non-overwintering larvae and adults were determined.The contents of fat,glycerol,trehalose and sorbitol in overwintering larvae were significantly higher than those in non-overwintering larvae,and there were no significant differences in the contents of water,glycogen and protein.The contents of glycogen,glycerol,trehalose and sorbitol in overwintering adults were significantly higher than those in non-overwintering adults,and there were no significant differences in water,fat and protein.The contents of fat,glycogen,glycerol,trehalose and sorbitol in overwintering larvae and adults were significantly different,while the contents of water and protein were not significantly different.There were significant differences in water,glycogen and trehalose contents between non-overwintering larvae and adults,but no significant differences in fat,glycerol,protein and sorbitol.3?The role of three protective enzymes,catalase(CAT),peroxidase(POD)and superoxide dismutase(SOD)in overwintering larvae and adults was clarified.The activity of three enzymes in overwintering larvae is lower than that in non-overwintering larvae.The activity of three enzymes in overwintering adult is higher than that in non-overwintering adult.The three enzymes in overwintering larva and adult are significantly different,and the enzyme activity in adult is significantly higher than that in larva.POD activity was significantly different between non-overwintering larva and adult.Enzyme activity in larva was significantly higher than that in adult,but CAT and SOD had no significant difference.4?The composition and variation of intestinal microorganisms of D.valens larvae in different periods were clarified.At the phylum level,the larval intestinal fungal community is mainly composed of Ascomycota,Chytridiomycota,Basidiomycota,and Rozellomycota.Ascomycota is the dominant phylum in three periods.At the genus level,Cyberlindnera is the dominant intestinal fungi.Larva intestinal bacterial communities are mainly composed of Bacteroidetes,Actinomycetes,Firmicutes,Proteobacteria and Chloroflexi.Proteobacteria is the dominant bacteria in three periods.At the genus level,the dominant genus of intestinal bacteria is Enterobacter.The diversity of intestinal fungal and bacterial communities is not the same in the three periods.The abundance of intestinal fungal communities is higher in May,while the abundance of bacteria is higher in January.This study could be a valuable contribution to understanding the spread of D.valens and its internal regulation mechanism during overwintering.At the same time,under the general trend of global warming,further explanation of its adaptability has theoretical guide for its scientific prevention and control.