Role of digestive protease enzymes and related genes in host plant adaptation of a polyphagous pest,Spodoptera frugiperda

The evolutionary success of phytophagous insects depends on their ability toefficiently exploit plants as a source of energy for survival.Herbivorous insects largelydepend on the efficiency,flexibility,and diversity of their digestive physiology and sophistication of their detoxification system to use chemically diverse host plants as foodsources.The fall armyworm,Spodoptera frugiperda(J.E.Smith),is a polyphagous pest ofmany commercially important crops.To elucidate the ability of this insect pest to adaptto host plant mechanisms,we evaluated the impact of primary(corn)and alternate(rice)host plants after 1l generations on gut digestive enzymatic activity and expression profiles of related genes.Results indicated that the total protease and classspecific trypsinand chymotrypsinlike protease activity of S.frugiperda significantly differed among hostplant treatments.The classspecifiq protease profiles greatly differed in S.frugiperdamidguts upon larval exposure to different treatments with inhibitors compared with treatments without inhibitors.Similarly,the single and cumulative effects of the enzymespecific inhibitors TLCK,TPCK,and E64 significantly increased larval mortality and reduced larval growth/mass across different plant treatments.Furthermore,the quantitativereverse transcription polymerase chain reaction results revealed increased transcription oftwo trypsin(SfTry3,SfTry7)and one chymotrypsin gene(Sfchym9),which indicatedthat they have roles in host plant adaptation.Knockdown of these genes resulted in significantly reduced mRNA expression levels of the trypsin genes.This was related to theincreased mortality observed in treatments compared with the dsRED control.This resultindicates possible roles of S.frugiperda gut digestive enzymes and related genes in hostplant adaptation.