| The English grain aphid,Sitobion avenae(Fabricius),is an economically important insect pest with worldwide distribution,and its host plants include various cereals and grasses in the Poaceae.In the process of long-term coevolution,symbionts and its host aphid S.avenae have formed close and mutualistic relationship.It has been shown that the species and infection frequency of secondary symbionts in aphid populations vary among areas and plants.But,further studies are needed in terms of their distribution,infection preference,relative abundance and inheritance mechanisms in host aphid populations.Meanwhile,with the climate change trend and UV radiation enhanced,there has been little research on the influence of secondary endosymbiont as "modulator" of its host aphid under different UV intensities.Our study used diagnostic PCR and 16S rDNA metagenome analysis for detection of microbial diversity in different parts of China.We also collected the life history data of S.avenae clones carrying three kinds of endosymbionts and their corresponding cured lines under three different UV treatments.The main results are as follows:1.Through analyzing 22 S.avenae samples collected from the province of Qinghai and Shannxi,there were six kinds of secondary endosymbionts identified:Hamiltonella defensa,Regiella insecticola,Rickettsia spp.,Serratia symbiotica,Spiroplasma spp.and X-type.Among the samples,the highest total infection rate was 88.9%,and the lowest was 11.1%.The infection rates of sach secondary endosymbiont among samples were different.Our samples were divided into three groups(i.e.,Shaanxi-2014,Shaanxi-2015,Qinghai-2015),and the infection rates of H.defensa showed no significant differences among the three groups;the infection rates of R.insecticola were significantly different among the groups,and Qinghai-2015 had a higher infection rate than Shannxi-2014.The infection rates of Rickettsia spp.in three group show significant difference also,the group of Qinghai-2015 significantly smaller than Shannxi-2015.S.symbiotica was not found in Qinghai-2015 group and was no significant difference in other group.Otherwise,multiple infection was found significantly higher in Shannxi-2015 than other two groups.2.Date from 16S rDNA metagenomic sequencing showed that bacterial communities in our samples were dominated by the phylum Proteobacteria,which had a mean relative abundance of 99.883%.At the family level,Enterobacteriaceae was the most dominant with a relative abundance of 90.721%.Buchnera,the primary endosymbiont of S.avenae,was the most abundance at the genus level.Among the top 35 most abundant OTUs at the geuns level,Rickettsia spp.and H.defensa were predominant in the group g1;Spiroplasma was the most abundance in the group g4;R.insecticola and Orientia in the group g5,whereas Buchnera and Ensifer were predominant in the group g6.Such results suggested qualitative and quantitative differences among S.avenae populations in microbial diversity.The correlation analysis indicated the relative abundance of Rickettsia spp.had positive correlations with annual low temperature,whereas Serratia had negative correlations with annual precipitation.3.The life-history data of S.avenae lines contain three kinds of secondary endosymbionts and their corresponding cured lines showed significant differences under different UV intensities.Under the high-intensity UV treatment,the total development time of nymphs for lines carrying H.defensa was higher than that of cured lines.This indicates that high-intensity UV radiation could reduce S.avenae's fitness.Under low-intensity UV treatments,the Rickettsia carrying lines showed shorter nymphal developmental time than cured lines,indicating some benefits for infected S.avenae lines.But,this benefit was not identified under high-intensity UV treatments.The life-history data on R.insecticola showed no significant differences between the infected and cured lines of S.avenae. |
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