Susceptibility Of Five Parasitoids To Seven Insecticides On Spodoptera Frugiperda Eggs

Spodoptera frugiperda(J.E.Smith)constitutes a migratory and invasive menace to rice and maize crops.Chemical control can be used as an emergency measure to control this pest,but it also poses a threat to natural enemies,environment and human health.Nevertheless,the ramifications of chemical insecticides on nature enemies have seldom been scrutinized,especially parasitoids,which are more sensitive to insecticides.Here we evaluated the toxicity and biological parameters related to adult and each developmental stage of four single insecticides(chlorantraniliprole,lufenuron,emamectin benzoate,spinetoram),a 3:1 amalgamation of chlorantraniliprole and lufenuron and two biological insecticides(Mamestra brassicae nuclear polyhedrosis virus and Bacillus thuringiensis)on three egg parasitoids species(Trichogramma mwanzai,Trichogrammatoidea lutea and Telenomus remus)introduced into Africa and two native Trichogramma species(Trichogramma dendrolimi,Trichogramma chilonis).In addition,the effects of seven insecticides on host selection and parasitism ability of five egg parasitoids and the differences in parasitism of parasitoids and the mortality of the adult parasitoids under different insecticide residue periods were also studied.To comprehensively evaluate the safety of several recommended insecticides against parasitoids and the sensitivity of the recommended insecticides to natural enemies.The main results are as follows:1.The results of the toxicity test of seven insecticides to adult parasitoids at the recommended doses in the field shows that the toxicity of spinetoram and emamectin benzoate is higher of T.mwanzai,T.dendrolimi and T.chilonis,the mortality is higher than 92.5%.A three-day emamectin benzoate treatment yielded 90% mortality for T.mwanzai,T.lutea,T.dendrolimi,and T.chilonis adults..The life span of five parasitoids treated with spinetoram and emamectin benzoate is the shortest.Although Mabr NPV and Bt do not kill parasitoids directly,they could shorten the life of parasitoids.Compared with control,the adult lifespan of T.lutea is prolonged after the combination treatment.A risk quotient analysis signified that the toxicity of Mabr NPV,Bt,chlorantraniliprole,and the 3:1 mixture to the quintet of tested parasitoid adults was the most minimal,succeeded by lufenuron.Emamectin benzoate and spinetoram were deemed moderately toxic to the egg and larval stages of all five investigated species.2.The developmental duration of five parasitoids at each stage is longer than that of the control group under Mabr NPV and Bt treatments,except egg stage of T.mwanzai and pupa stage of T.chilonis.Compared to the control and other treatments,T.mwanzai,T.dendrolimi and T.chilonis shows the lowest emergence rate under the treatment of spinetoram at each developmental stage,follows by emamectin benzoate treatment.Mabr NPV and Bt treatments significantly reduce the emergence rate of T.mwanzai at different developmental stages.Chlorantraniliprole has the lowest effect on the average emergence rate of the five parasitoids after treatment at each stage.3.There is significant differences in host selection and parasitic ability of parasitoids under different insecticide treatments.All of five egg parasitoids have obvious negative tendency to the host eggs treated with spinetoram under the treatment of recommended concentration.The mixture of chlorantraniliprole: lufenuron(C:L=3:1)and chlorantraniliprole have significant attraction to T.dendrolimus,and T.chilonis.The egg parasitized number of five parasitoids treat with spinetoram for 24 h is significantly lower than the control and other six insecticide treatments follows by emamectin benzoate treatment.After treatment with chlorantraniliprole,lufenuron,compound insecticide and two biological insecticides,there is no significant impact on the parasitism number of T.mwanzai,T.dendrolimi and T.remus.In addition,T.remus has the highest egg parasitized number among five parasitoids under control and seven insecticide treatments,while T.dendrolimi parasitized more host eggs than T.mwanzai,T.lutea,and T.chilonis.4.Except to T.remus,the different residual periods of the seven insecticides have significant effects on the mortality and parasitic ability of the other four parasitoids.The adult mortality rate of four parasitoids increase with the residual period time and decrease significantly under the treatment of the spinetoram and emamectin benzoate for 0-7 days.The adult mortality of T.mwanzai and T.dendrolimi is significantly highest on the first day of treatment with lufenuron.The parasitized number of the five parasitoids significantly increase of the residual period after treatment with spinetoram,but is significantly lower than that of the control in each residual period.The parasitism of T.lutea and T.remus increase with the prolongation of the residue periods of the two biological insecticides.The residual periods of chlorantraniliprole and the compound insecticide have no effect on the parasitism of T.remus.In summation,our observations imply that chlorantraniliprole,the 3:1 combination of chlorantraniliprole and lufenuron,and their residues albeit classified as innocuous to the adult and various developmental stages of T.dendrolimi and T.remus,followed by two biological insecticides.Lufenuron has a moderate risk to adult T.chilonis,but is safe for the other four parasitoids.particularly in contrast to chemical insecticides such as spinetoram and emamectin benzoate,which may pose harm to parasitoids.In addition,T.remus showed the lowest sensitivity to the seven recommended insecticides for the S.frugiperda,followed by T.dendrolimi.