Adaptive Mechanisms Of Oedaleus Asiaticus Bey-bienko (Orthoptera:Acrididae) To Food Plants

As an important ecological factor,plant can significantly influence insect population dynamics.Oedaleus asiaticus Bey-Bienko(OA),a significant grasshopper pest species occurring in north China,has specific food niche.Its outbreak is closely related to food distribution.Adaptive mechanisms of how foods drive OA migration and plague outbreaks are now still not clear.In the present study,we studied food adaptation of OA,revealed the ‘compromise selection' mechanism and explored the potential molecular mechanism of food adaptability by the study of insect insulin-like signaling pathway(ILP).Results showed that:?.Ecological adaptation of OA to food plants determined its occurrence and distribution.OA relative density exhibited a significant negative relationship to Leymus chinensis above-ground biomass,and had significant positive relationship to the above-ground biomass of Stipa krylovii(Sk)and total above-ground plant biomass,respectively.OA had significantly greater survival rate and growth rate in Stipa-dominated grassland.When presented with Sk,OA also had significantly higher growth rate,approximate digestibility(AD),efficiency of conversion of ingested food(ECI)and efficiency of conversion of digested food(ECD)with largest consumption amount.Nevertheless,OA feeding A.frigida(Af)and C.microphylla could not complete life history.Preferable diet and not preferable diet acted as the ‘push-pull',drive OA migration and plague outbreaks.?.Physiological adaptation of OA to food plants determined the ‘compromise selection' mechanism for detoxification and nutrition demand.Compared to Af or Lc,Sk acted as the optimal food resource for low secondary metabolites(flavonoid,tannin,phenol,alkaloid,terpenoid)and high nutrition(starch,lipid,crude protein),contributed to increased overall performance and digestive enzyme activity of OA,and the decreased ROS concentration and detoxifying or protective enzymes activity.The essence of OA migration and plague outbreaks followed the ‘compromise selection' regulation of highest nutrition intake and lowest detoxification cost.?.Gene adaptation of OA to food plants was the basis of physiological adaptation.The OA gut that fed on SK had the largest variation in gene expression profiles with a total of 88 genes significantly up-regulated compared to those feeding on the other three plants.Those genes were belonged to protein,carbohydrate and lipid digestion or utilization.There were total 299 differentially expressed genes in OA body fed on A.frigida compared to those fed on other food plants.Total 166 genes of insect cuticle biosynthesis,DNA replication and energy metabolism were significantly down-regulated.Total 133 genes of detoxification,stress-resistance and signal transduction were significantly up-regulated.?.OA utilized food plant to regulate growth by ILP.Plant nutrition,glycoside and other detoxification metabolites could mediate ILP,which provided the potential molecular mechanism to regulate insect growth.Similarly,the gene expression and protein phosphorylation level of INSR?IRS?PI3K?AKT in ILP pathway,were significantly up-regulated in OA when confronted with the optimal food Sk.Consequently,the actived ILP contributed to OA growth.Nevertheless,food plant Af had the opposite effects to OA.That is,OA has evolved into active mechanism using food plant to adapt wider ecological area.This could reveal why OA was the most distributed species and easily outbreak in Inner Mongolia,China.This study revealed the principle of chemical ecology and molecular ecology of grasshopper food adaptability,and provided theoretical basis for grasshopper sustainable control.