Effects On Population Parameters,Epidermis And Chitin Synthase Of Sitobion Avenae (Fabricius) Exposed To Long-term UV-B Stress

Global warming and increasing ultraviolet can bring about strong selection pressure on organism.Because short-term（several generations or months）UV stress can directly or indirectly affect growth,development,reproduction and genetic variation of creatures,but the effects of long-term UV stress（dozens of generations or perennial）on organisms have rarely been reported.Sitobion avenae（Fabricius）is an important pest on wheat.It has short generation time,strong fecundity and typical characteristics of r countermeasure,it also has a strong ability to adapt to environment changes.So it is an ideal material for studying the effects of long-term environmental stress on organism.It is unclear how the aphids adapt and its genetic variation under long-term UV stress.At the same time,since insect epidermis is an important part that was directly exposed to ultraviolet radiation,its morphology and structural changes are still unknown;and chitin,which is one of the main components of insect epidermis,one of the synthetases--CHS1,its changes has rarely been reported under long-term UV stress.In the previous period,our experimental team has been studied the adaptability of S.avenae from 1st generation to 37th generation exposed to long-term stress of different UVB intensity,it need further research whether the adaptability and growth change of the subsequent generations of S.avenae is consistent with the previous.Therefore,this study used S.avenae after the 40th generation as test material,studied the changes about population parameters,the morphological structure of the abdomen epidermis and the relative expression level of chitin synthase 1（CHS1）of S.avenae.According to the previous study of our lab,we has selected the UVB intensity of 0.5mW/cm² and 0.7 mW/cm² as the key doses affecting aphids,to ensure consistency and sustainability of research,we adopted the same treatment intensity and time,continued to explore the change of population parameters under control group and treatment groups about45th,51st,57th,63th,68th and 73rd generations of S.avenae;Besides,observed the morphology and structure of the epidermis of 68th S.avenae by scanning electron microscopy and transmission electron microscopy.In addition,the relative transcript level of chitin synthase 1（CHS1）about 54th,59th,64th and 69th generations of S.avenae was determined by Real-time PCR.Above research aims to provide a theoretical basis for the ecological inheritance and evolution of S.avenae under long-term UVB stress.At the same time,it also provides a theoretical basis for the impact of increased UVB intensity caused by environmental pollution on the ecological environment.The experimental results are as follows:1.The changes of population parameters of different generations S.avenae under different UVB intensityUnder high-intensity or low-intensity treatment,with the increase of generations the intrinsic rate of increase（r）,the finite rate of increase（λ）and the net reproductive rate（R₀）of S.avenae all gradually declined;The average longevity,fecundity and Ovi-days also showed a gradual decline trend,and the value of the treatment group was significantly lower than that of the control group with the increase of generations;under the same UVB intensity,the value of age-specific survival rate（lx）of the 45th generation in treatment group was higher than that of the control group,but the situation of 73rd generation was the opposite of 45th generation.Furthermore,the value of r between the low-treatment groups showed a trend of decline,firstly rapid,then gentle finally rapid again,and the values of the 13 consequent generations did not change much;the value of r in the high-treatment group showed a trend of decline,firstly rapid,then slow and next rapid,and the values of 11 consequent generations that kept rising.2.Observation results of morphological structure on abdomen epidermis under different UVB intensityThe results observed by scanning electron microscopy（SEM）showed that S.avenae in the control group had a small amount of desquamation on the outermost layer of the epidermis,but the same position in the treatment group was more densely distributed lamellar structures,and these desquamation were not evenly distributed on the outermost surface of the epidermis,it seemed that waxy layer was broken down,and the lamellar structure under high intensity treatment was larger.Secondly,there were relatively more water-like substances around the setae of two treatment groups,but this phenomenon was not obvious in the control group.The results observed by transmission electron microscopy（TEM）showed that,the cuticle layer of S.avenae is thinnest in the control group,had 7 layers,and the low-treatment group is second,had 9 layers,but the high-treatment group is thickest,had 14 layers.In addition,the ratio of thickness between cuticle layer and dermis in the treated group was significantly greater than the control,which was 2 and 3.5 times that of the control group respectively,and the thickness of dermis in the treatment group was only third of the control group.3.The change of relative transcript level of chitin synthase 1（CHS1）of S.avenae under different UVB intensityBetween different generations,the relative transcript level of CHS1 in the high-treatment group were generally higher than that of the low-treatment group and the control group.With the increase of generation,there was no significant difference in relative transcript level of CHS1 between different generations in the control group,and the expression level of CHS1both decreased at first and then increased in the high-treatment group and low-treatment group.And the highest expression level were both seen on the 54th generation.In summary,aphids are exposed to UV stress,the longer the generation,the more significant the effect,and the survival rate and fecundity is lower.Long-term UVB irradiation can destroy dermal cells and significantly affect the relative expression of CHS1.