The Adaptability And Physiological Mechanisms Of Spodoptera.Frugiperda To Eleven Host Plants In Fujian Province

Spodoptera frugiperda is one of the most destructive migratory pests in the world and is native to tropical and subtropical regions of the Americas.Spodoptera frugiperda is a polyphagous pest with more than 350host plants.Among them mainly are the Poaceae plants,which account for about 1/3 of the total host plants.Since its invasion into Yunnan,China in January 2019,it has been rapidly spreading across most cities and regions of the whole country,and damaging 22 crops,including maize in the field,posing a serious threat to China’s agricultural production.Eleven potential host plants of S.frugiperda in Fujian Province were selected,which as test plants to explore the adaptability and physiological mechanism of the S.frugiperda to different hosts.Including maize Zea mays,rice Oryza sativa‘Quanyou 212’（hybrid rice）,and Oryza sativa‘IR203-1’（glutinous rice）,adlay Coix lacryma-jobi‘Cuiyi 1’and‘Puyi 6’and bermudagrass Cynodon dactylon,Cabbage Brassica oleracea,peanut Arachis hypogaea‘Quanhua1’and‘Fuhua 8’,soybean Glycine max,and sweetpotato Ipomoea batatas.The main research findings are as follows:（1）The adaptability of S.frugiperda to 11 potential host plants in Fujian Province.Spodoptera frugiperda completes its life history on all tested plants.However,compared with S.frugiperda fed on Z.mays,S.frugiperda fed on the other ten plants had a longer larval development time and mean generation time（T）,but a reduced weight of the 5^th instar larvae,a lower fecundity（the average number of eggs laid by per female）,and a lower value of the intrinsic rate of increase（r）,the finite rate of increase（λ）and net reproductive rate（R₀）.In addition,the last instar larvae of S.frugiperda fed on Z.mays s were the 5^th or 6^th instar,with a proportion of22.4%and 77.6%,respectively.While the last instar larvae of S.frugiperda fed on the other ten plants were from the 6^th to the 8^th instar,the proportion of supernumerary larvae(molt beyond the 6^th instar)ranged from 4.9%to70.8%.（2）Physiological response characteristics of S.frugiperda fed on 11host plants in Fujian Province.Compared to the 4^th instar larvae of S.frugiperda fed on Z.mays,the 4^th instar larvae of S.frugiperda fed on B.oleracea had higher trypsin activities,lipase activities and GSTs activities;those larvae fed on G.max had higher amylase activities and lipase activities;those larvae fed on A.hypogaea‘Quanhonghua 1’had higher amylase activities,GSTs activities,and ecdysone titers,but had lower juvenile hormone（JH）titers;those larvae fed on A.hypogaea‘Fuhua 8’had lower ACh E activities;those larvae fed on C.lacryma-jobi‘Cuiyi 1’and‘Puyi 6’had higher lipase activities;those larvae fed on O.sativa‘Quanyou 212’had higher ecdysone titers;those larvae fed on O.sativa‘IR201-3’had lower JH titers in adult females;those larvae fed on C.dactylon had higher lipase activities and lower ACh E activities;those larvae fed on I.batatas had higher lipase activities,CYP 450 activities and ecdysone titiers,but had lower ACh E activities.Except for those adult males fed on A.hypogaea‘Fuhua 8’,the ecdysone titers in adult males fed on other nine tested plants were significantly lowered compared to those fed on Z.mays.（3）The relationships between the phenotype and physiological response characteristics（including the enzyme activities and hormone titers）of S.frugiperda,and host phytochemical characteristics of S frugiperda.According to redundancy analysis,the larval development time and pupae development time were significantly correlated with the lipase activities,amylase activities and the ecdysone titers of the 4^th instar larvae,which were significantly correlated with the amount of total phenols and terpenoids in host plants.The preadult survival rate was significantly correlated with the amylase activity,which was significantly and positively affected by the amount of proteins and free fatty acids,and negatively affected by the amount of tannin.The fecundity was significantly correlated with the CYP 450 activities,which was significantly and positively affected by the amount of proteins and free fatty acids,and negatively affected by the amount of tannins,flavonoids and terpenes.（4）The adaptability and physiological response characteristics of S.frugiperda in response to continuous rearing.After being continuously reared for eight generations on two kinds of C.lacryma-jobi and A.hypogaea,the development time of larvae and pupae,the fecundity（the average number of eggs laid by per female）,r,λ,R₀ were all significantly improved,the proportion of supernumerary larvae decreased from 32.6%-77.2%to 10.2%-26.0%,and the proportion of 6^th instar last larvae increased from 21.7%～73.1%to 75.0%～90.2%.The development time of pupae,preadult survival rate,r,and R₀ were no significant difference between eight generations of S.frugiperda feeding on two kinds of C.lacryma-jobi and two generation of S.frugiperda feeding on Z.mays.No matter which host plant was fed continuously,the lipase activities and ACh E activities of the 4^th instar larvae of S.frugiperda in the F2,F5 and F8 generations showed an upward trend.In summary,Z.mays is the most suitable host plant for S.frugiperda,followed by A.hypogaea‘Quanhua 1’and‘Fuhua 8’,I.batatas,C.lacryma-jobi‘Cuiyi 1’and Puyi 6,C.dactylon,and O.sativa‘Quanyou212’.Brassica oleracea,G.max and O.sativa‘IR201-3’are the least suitable host plants for S.frugiperda.The adaptability of S.frugiperda to two kinds of C.lacryma-jobi and A.hypogaea is substantially improved by continuous rearing for eight generations.Three nutrients（protein,reducing sugars,and free fatty acids）and five secondary substances（terpenoids,flavonoids,tannins,alkaloids and total phenols）of the host plant are the main factors affecting the enzymatic activities,hormone titers and phenotype of S.frugiperda.Spodoptera frugiperda adapts to its host by adjusting enzyme activities and hormone titers.