Comparative transcriptional analysis provides insights of possible molecular mechanisms of wing polyphenism induced by postnatal crowding in Aphis gossypii

Background:Aphis gossypii is a worldwide sap-sucking pest with a variety of hosts and a vector of more than 50 plant viruses.The strategy of wing polyphenism,mostly resulting from population density increasing,contributes to the evolutionary success of this pest.However,the related molecular basis remains unclear.Here,we identified the effects of postnatal crowding on wing morph determination in cotton aphid,and examined the transcriptomic differences between wingless and wing morphs.Results:Effect of postnatal crowding on wing determination in A gossypii was evaluated firstly.Under the density of 5 nymphs·cm-2,no wing aphids appeared.Proportion of wing morphs rised with the increase of density in a certain extent,and peaked to 56.1% at the density of 20 nymphs·cm-2,and reduced afterwards.Then,transcriptomes of wingless and wing morphs were assembled and annotated separately to identify potentially exclusively or differentially expressed transcripts between these two morphs,in which 3 126 and 3 392 unigenes annotated in Nr(Non-redundant protein sequence) database were found in wingless or wing morphs exclusively.Moreover,3 187 up-and 1 880 down-regulated genes were identified in wing versus wingless aphid.Pathways analysis suggested the involvement of differentially expressed genes in multiple cellular signaling pathways involved in wing morphs determination,including lipid catabolic and metabolism,insulin,ecdysone and juvenile hormone biosynthesis.The expression levels of related genes were validated by the reverse transcription quantitative real time polymerase chain reaction(RT-qPCR) soon afterwards.Conclusions:The present study identified the effects of postnatal crowding on wing morphs induction and demonstrated that the critical population density for wing morphs formation in A gossypii was 20 nymphs·cm-2.Comparative transcriptome analysis provides transcripts potentially expressed exclusively in wingless or wing morph,respectively.Differentially expressed genes between wingless and wing morphs were identified and several signaling pathways potentially involved in cotton aphid wing differentiation were obtained.

On the systematic position of Cacosyndya Kirby(Hymenoptera:Tenthredinidae)with redescription of Cacosyndya dimorpha Freymuth

A peculiar sawfly genus from middle Asia,Cacosyndya Kirby,1883 and the type species Cacosyndya dimorpha(Freymuth,1870)are redescribed and illustrated.The systematic position of this genus in Tenthredinidae is discussed.The females in the genus are apterous,the only known apterous Symphytan,but the male is normally winged.Cacosyndya is not a member of Fenusinae or Heterarthrinae,but a member of Phymatocerini of Blennocampinae,Tenthredinidae as shown by the structure of the antenna,wing venation and body structure.The relationship between Cacosyndya and members of Phymatocerini is briefly discussed.