Effects On Wax Synthesis Of Phenacoccus Solenopsis By Spirotetramat And Its Mechanism

Phenacoccus solenopsis is a worldwide pest with strong adaptability of invation and can cause serious crop and forest loss.Its surface has a layer of wax powder,and can resist water loss and natural enemies' predation.In addition,the wax layer affects the effect of insecticides and make it difficult to control.At present,most of the studies on the p.solenopsis are focused on the biological characteristics and laboratory bioassay.Spirotetramat is effective in controlling sucking pests and acts on its target acetyl-Co A carboxylase(ACC),which is the rate-limiting enzyme in the lipid synthesis pathway.The wax powder is reduced after spirotetramat and the natural defense layer is destroyed.Few researchers have explored the effect of such insecticides on the synthesis of wax ester.In this study,the third instar nymphs of P.solenopsis were treated with spirotetramat in leaf dipping method.The toxicity of the nymphs was observed,and the samples were collected for transcriptome sequencing and analysis.A transcriptome analysis was conducted to reveal the mechanism associated with wax synthesis of p.solenopsis by spirotetramat.Meanwhile,several genes showing different expression by spriotetramat and are associated with wax ester biosynthesis were cloned.Physicochemical properties of the very long-chain fatty acid elongase gene(ELO)and fatty acid desaturase gene(FAD),and their expression levels in different developmental stages of the scale were analyzed.The main results are as follows:1.After treated with spirotetramat,the wax powder of P.solenopsis decreased obviously and the growth and development were inhibited.A solexa sequencing was performed on the P.solenopsis after spirotetramat treatment,and total of 78302 unigenes were obtained,of which 10208 were unigenes with e<1e-5 in Blast results,and there were 652 genes associated with lipid metabolism.Compared with the control group,1969 unigenes were changed after the p.solenopsis treated with spirotetramat.Classified according to the difference of genes involved in KEGG pathways,mainly related to wax esters biosynthesis pathway include biosynthesis of unsaturated fatty acid,fatty acid biosynthesis,fatty acid degradation and fatty acid elongation,etc.The qRT-PCR validation of the differential genes showed a trend consistency of 81.25%.2.The genes PsELO1 and PsELO2 were cloned and their ORFs were 810 bp and 1041 bp,the sequence characteristic analysis and the change of expression in different development stages were carried out.PsELO1 was a hydrophobic,non-secreted,unstable protein and PsELO2 was hydrophilic,secretion,unstable protein.The expression of PsELO1 was the highest in the oviposition stage of female adult and the lowest in the first instar nymph stage and female adult stage.PsELO2 expression was the highest in the third instar nymph stage,but stable in the whole developmental period.The expression of PsELO1 was up-regulation and PsELO2 expression was down-regulated after the treatment with spirotetramat.3.The gene PsFAD1-4 were cloned and the ORFs were 1239 bp,1080bp,1053 bp,and 849 bp,The sequence characteristic analysis and the change of expression in different development stages were carried out.PsFAD1-3 was a hydrophilic non-secreted stable protein and PsFAD4 was a hydrophilic,non-secreted,unstable protein.The expression level of PsFAD1 was lower in female adults stages.The expression level of PsFAD2 was highest in the oviposition period of female adults.The expression level of PsFAD3 showed a downward trend throughout the developmental period,but the change was not significant;the expression level of PsFAD4 was higher in the second instar stage,and the expression level was lowest in females during the oviposition period.The expression of PsFAD1-4 were up-regulated to varying degrees after the treatment with spirotetramat.