Preliminary Mechanism Study Of The Wing Morph Differentation In Rhopalosiphum Padi

Rhopalosiphum padi(L.)is one of the most important pests on wheat in China.It can damage wheat by sucking the juice,meanwhile the pest can also transmit the barley yellow dwarf virus,causing serious losses to the production of wheat every year.Adults of R.padi can generate winged and wingless offspring depending on environmental changes.The wingless R.padi has larger ovaries for reproduction,while the winged R.padi has stronger flight muscles and wings for migration.Wing ployphenism provides advantage for its adaptation to complex environments,and benefits for its diffusion,reproduction and avoidance of natural enemies,which is an important survival strategy for R.padi;the population diffusion of R.padi is also related to wing morph differentation,but the mechanisms underlying this phenomenon remain to be further studied.Further study on the wing ployphenism mechanism of R.padi can not only provide information for population diffusion of R.padi,but also improve the understanding of molecular mechanisms of wing ployphenism.In this study,the maternal population density for wing morph differentitation of offspring was determined;effects of different maternal crowding durations on wing morph differentitation of offspring was analyzed;the titers of ecdysone,juvenile hormone and insulin titer after crowding and starvation treatment were measured by enzyme-linked immunosorbent assay(ELISA);the coding region of ecdysone signal pathway related genes was obtained;the expression of ecdysone signal pathway related genes was analyzed by real-time quantitative PCR.The results are as follows:1. Effects of maternal population density on the wing morph differentiation of R.padi offspringBy setting different population density,we observed the percentage of winged progeny of R.padi in five days.The results showed that neither solitary treatment nor starvation treatment can not change the offspring wing morph.More than 30%offspring are winged morphs after 6 individuals/cm~3 stress treatment;after 15 individuals/cm~3 stress treatment,the proportion of winged offspring reached 45%.The density of 15 individuals/cm~3 is considered as a suitable population density for wing ployphenism analysis of R.padi under our experimental conditions.2. Effects of different maternal crowding time on wing morph differentiation of R.padi offspringAfter different crowding(15 individuals/cm~3)time,the percentage of winged progeny of R.padi in five days were observed.The results showed that more than 10%of offspring were winged morphs after 3 hours crowding treatment;after 6 hours crowding treatment,the proportion of winged offspring were significantly increased to more than 30%;after 15hours crowding treatment,the proportion of winged offspring reached 48%,the proportion of winged offspring is significantly higher than the 12 hours treatment,but no significant difference compared with 18 hours treatment.It is considered that 15 hours crowding treatment is the window period of wing morph diffrentiation.3. Effects of crowded and starvation stress on fecundity of R.padiThe fecundity of R.padi in five days was 36.51±0.62 under individual feeding condition and was 34.34±0.95 under individual rearing without feeding,which were significant higher than the fecundity(30.28±0.73)in five days under 15 hours treatment with density of 15 individuals/cm~3.The results indicated a fitness cost associated with wing differentation of R.padi.4. Effects of crowded and starvation stress on hormone titer of R.padiThere was no significant change in juvenile hormone and insulin titer after 24 hours crowding treatment with the density of 15 individuals/cm~3,whilst ecdysone titer was decreased significantly.The titers of juvenile hormone and insulin was decreased significantly after starvation treatment,whilst ecdysone titer was not significantly changed.There was a negative correlation between ecdysone titer and crowding durations.Ecdysone might be involved in the wing morph differentiation of R.padi.5. Effect of crowded stress on ecdysone signal pathway related genes of R.padiExpression of 12 ecdysone pathway related genes of R.padi were varied under the conditions of individual rearing without feeding and crowding rearing without feeding.There was no significant difference in Rp-Ptth gene expression level between different treatment;Rp-Ptsp gene was up-regulated under rearing without feeding;Rp-Ec R gene and Rp-Usp gene showed similar expression level,but Rp-Ec R gene was down regulated in crowding and Usp gene was not down regulated;Rp-E74 gene was down regulated in crowding treatment;expression of Rp-EH were significantly up-regulated in the crowding treatment.The results indicated the change of ecdysone pathway related genes expression is related to the wing morph differentation of R.padi.