Biological Basis Of Sterility Of Spodoptera Frugiperda Irradiated By X-ray

Spodoptera frugiperda,a major agricultural pest native to the Americas,has spread to Africa,Asia and Australasia,posing a serious threat to global food production security.The Sterile insect technique（SIT）is a safe,effective,and widely applicable pest control technique that uses sterile insects to eradicate invasive pests.However,there has not been any extensive research on its application to prevent S.frugiperda.In determining the proper dose and percentage of radiation infertility insects,the effects of various X-ray radiation doses on the biological and reproductive parameters of S.frugiperda were studied in this study.Finally,studies were explored the potential molecular mechanism of radiation-induced sterility of S.frugiperda.The main results are as follows:1.Effect of X-ray irradiation on biological parameters of S.frugiperda at different developmental stagesS.frugiperda eggs,larvae,3-day-old pupae,5-day-old pupae and 8-day-old pupae were irradiated with doses ranging from 50 to 400 Gy.The mortality of the irradiated insects and the mating rate and reproductive parameters of emerged adults were measured.The results showed that the tolerance of eggs and larvae to irradiation was low.The results showed that eggs and larvae had low X-ray tolerance,eggs had a mortality rate higher than 92%,larvae had a mortality rate greater than 64%,and the mating rate of adults（12.5%-60%）decreased significantly than that of control.At 3 and 5 days of age,the pupae exposed to 50 Gy had a higher emergence rate（3days:93.33%;5days:40%）,but a lower mating rate（21.67%-50.00%）and a similar infertility rate（22.84%-51.49%）compared with the control（13.14%-24.72%）.However,the radiation dose of 50-350 Gy had no significant effect on the survival rate of 8-day-old pupae,and the mortality and malformation rate were less than 15%,and the mating rate conpared to the control was no significant different.Studies have shown that 8-day-old pupae are suitable for irradiation.The 8-day-old female and male pupae of S.frugiperda were irradiated with 50-400Gy X-rays,and the reproductive parameters of the adults after mating were tested.After the male pupae were irradiated with 50-400 Gy,the mating rate and oviposition period of the male insect had no significant change compared with the control,but the irradiation had a significant effect on the reproductive parameters of the female moth.When the irradiation dose was more than300 Gy,the mating rate（53%-64%）and oviposition（0.75-0.91 d）of the irradiated females decreased significantly.The radiation sensitivity of female was higher than that of male,and the sterilization dose of female was 400 Gy,but that of male was higher than that of 400 Gy.The logistic curve fitting results showed that the substerile dose of male moths was about 250Gy,and the infertility rate could reach 88%after irradiation.This dose can be used in the follow-up study on radiation sterility of S.frugiperda.2.Effect of irradiation on the offspring of S.frugiperdaAfter 250 Gy irradiation,only 11%of the offspring of male pupae mated with normal insects could develop to the adult stage,and the F₁ generation adults were also partially infertile.The number of eggs laid was significantly reduced,the sex ratio was inclined to male,and the infertility rate was 40%.The number of eggs laid by the F₂ generation was also lower than that of normal insects,the proportion of eggs developing to adults was lower（33%-40%）,and the sterility rate was higher（42%-66%）than that of the F₁ generation.3.Effectiveness of field control of S.frugiperda exposed to X-ray irradiationIn this study,the 8-day-old pupae of S.frugiperda were irradiated with 50-350 Gy dose,and the flight ability of adults after eclosion was tested.The male pupae of S.frugiperda were irradiated with 250 Gy of X-rays,and the effects of the release ratio and age of irradiated males on the sterility of offspring were measured.The effects of different release ratio of males on the control of S.frugiperda were evaluated by a cage experiment in the field.The results showed that X-ray irradiation reduced the flight time of males,but had no significant effect on flight speed,and the dose of 250 Gy had no significant effect on the flight ability of males.When the ratio of irradiated males to normal males reached 12:1,the hatching rate of S.frugiperda eggs could be reduced to less than 26%,and there was no significant difference in the mating competitiveness of irradiated males at different ages.In the field cage experiment,when the release ratio of irradiated males to normal males was 12:1-20:1,the protection rate of maize leaves reached 48%-69%,and the insect decline rate reached 58%-83%.4.Effects of X-rays on the flight and mating competitiveness of S.frugiperdaIn this study,8-day-old Spodoptera frugiperda males were irradiated with 50-400 Gy of X-rays.The developmental parameters of testes and ovaries were observed after emergence.The results showed that the reproductive system of S.frugiperda was greatly affected by irradiation.The ovarian development of S.frugiperda was slowed down with the increase of irradiation dose,and the pre-mature stage of ovaries was longer than that of normal insects.The sensitivity of testes to irradiation was lower than that of the female.The development speed of testes of irradiated males was lower than that of the normal insect at the early stage of adult（1-2 d）,while the size of testes of irradiated males was close to that of the normal insect at the 3-8 d of adult.5.Effect of X-ray irradiation on gene expression of Spodoptera frugiperdaDifferentially expressed genes were analyzed in irradiated pupae and irradiated adults at the pupal stage of S.frugiperda.The total reading of sequencing was 1130344324,and a total of 169.55 G data were obtained.Using FDR<0.05 and|Log₂FC|>1 as the condition,the TPF vs NPF,TPM vs NPM,TAF vs NAF,TAM vs NAM selected in the comparison group,346,401,691,544 differentially expressed genes.Functional enrichment analysis of GO and KEGG showed that the differentially expressed genes were significantly enriched in GO items such as response to oxidative stress and response to stress between irradiated pupa and normal pupa.KEGG pathway analysis showed that the differential genes of irradiated male and female pupae were significantly enriched in lysosome and steroid hormone biosynthesis pathways.Compared with normal insects,the differential genes of irradiated adult pupae were significantly enriched in cytochrome P450,regulation of actin cytoskeleton and other pathways.The differential genes in all comparison groups were enriched in DNA biosynthesis and vitellin-related hydrolase pathway.In conclusion,S.frugiperda could meet the requirements of radiation sterility using X-ray irradiation,with the optimal radiation dose of 250 Gy for 8-day-old pupae.Under this dose,the infertility rate of both sexes reached more than 85%,and the offspring of males also inherits some infertility characteristics,resulting in a sustainable decline in the population.The ideal control effect could be achieved when the ratio of 250 Gy irradiated males to normal males was12:1,and the control effect in the field was similar to that of insecticides.In addition,the developmental parameters of testes and ovaries of both sexes were measured after irradiation,indicating that irradiation could delay the development of the reproductive system of both sexes.Analysis of differential gene expression changes after irradiation further revealed a significant effect of irradiation on the gene expression of S.frugiperda.This study provided basic data reference and theoretical verification for the large-scale application of the irradiation sterility technique of S.frugiperda,provided reproductive data reference for the large-scale release and recycling of irradiated insects,and provided support for further exploring the infertility mechanism of X-ray-irradiated insects.