Basic Research On The Application Of ⁶⁰Co Irradiation In The Control Of Spodoptera Frugiperda

Spodoptera frugiperda,is an important migratory pest of the order Lepidoptera,family Noctuidae,genus Spodoptera,that attacks 353 host plants including corn,rice,and sorghum among other agricultureal crops.The insect has strong reproductive and migration ability posing a constant risk of outbreak at any time.At present,the use of chemical insecticides is served as one of the most commonly used emergency measures to control S.frugiperda,however,it is unfriendly to the environment,and easy to generate pesticide resistance.So there is an urgent need for a more convenient,effective,and environmentally friendly prevention and control technology to improve control effect.Sterile insect technique（SIT）has attracted much attention due to its strong specificity,absence of resistance level development,and sustainable effects in pest control.In this paper,⁶⁰Co-γray was selected as the radiation source to study the effects of different doses of irradiation of S.frugiperda on the offspring of laboratory population and its offspring population.The main results are as follows.1.Effects of ⁶⁰Co irradiation on the development and reproduction of inbreeding population of S.frugiperdaThe eclosion rate,wing deformity rate,longevity,fecundity and hatching rate of offspring eggs of S.frugiperda populations at 100,200,250,300,350,400,and 500 Gy were compared.The results showed that the eclosion rate of S.frugiperda adults decreased with the increase of irradiation dose.The eclosion rates under 250,350,400,and 500 Gy irradiation decreased to 72.8%,69.4%,69.4%,and 50.6%,respectively,which were significantly different from the control group（91.7%）.The average longevity of female and male adults was shortened with the increase of irradiation dose.It was shortened from 12.5d and 10.2 d in the control group to 3.8 d and 3.4 d in the 500 Gy treatment group,respectively.and the longevity of female and male adults in the irradiation post-treatment group was significantly lower than that in the control group.The male and female of S.frugiperda were paired with each other at the same irradiation dose.It was found that the sterile dose of the self-pollinated population of S.frugiperda was 200 Gy.At this dose,the female of S.frugiperda could still lay eggs,but are unable to hatch out.At the irradiation dose of 300-500 Gy,the parent female did not lay eggs.In addition,when the irradiation dose was 350 Gy,the average longevity of female adults was 8.0 d,which was significantly lower than that of the control（12.5 d）,but it was longer than that of female adults irradiated below this dose.2.Analysis of the development and reproduction of the male-irradiated and female-irradiated population of S.frugiperda by two-sex life tableThe irradiation doses were set at 10,25,50,100,200,250,and 350 Gy,and the female and male pupae were irradiated respectively.After outcrossing with the opposite sex insects without irradiation treatment.It was found that 200 Gy female irradiated population and250 Gy female irradiated population could lay eggs but could not hatch,and 350 Gy male irradiated population did not lay eggs,indicating that 200 Gy was the sterile dose of the female irradiated population and 350 Gy was the sterile dose of the male irradiated population.And the egg hatching rate of the outcrossing offspring population decreased with the increase of irradiation dose.The egg hatching rate of the control group was 89.1%,which was significantly higher than 72.2%,73.8%,and 76.1%of the 250IM（250 Gy irradiation male with no-irradiation female population,the same abbreviation as follows）,200IM and 100IM treatment groups.Compared with the control group,the pre-adult durations of 50IM,50IF,25IF,and 10IF treatment groups were 31.8 d,32.2 d,31.0 d,and32.6 d,respectively,which were significantly shorter than that of the control group（33.5d）.The pre-larvae duration of the 250IM group was significantly longer than that of the control group,which was 35.1 d.The pre-adult survival rates of 250IM,200IM,and 100IF groups were 17.8%,10%,and 15.5%,respectively,which were significantly lower than that of the control group（50%）.However,the highest r value in the outcrossing population of S.frugiperda was in the 10IF group,followed by the 10IM group,and the corresponding values were 0.1709 and 0.1634,respectively,which were slightly higher than the control group（0.1496）.After 120 days,the number of offspring of male and female parents treated with 10 Gy and female parents treated with 50 Gy will reach 1 174 050 840.75,2 054 812361.27,and 366 657 831,respectively,which is higher than the control group of 241 752311.27 offspring,indicating that low-dose irradiation may have a certain role in promoting.3.Assessment of starvation tolerance and flight ability on released population of ⁶⁰Co irradiated S.frugiperdaS.frugiperda male were irradiated at 300 Gy,female at 150 Gy,and both no-irradiated male and female were used as control.It was found that without any food and water,the male irradiated at 300 Gy and the no-irradiated male all died on the 10th day and 6th day,and the female moths irradiated at 150 Gy and the no-irradiated female died on the 10th and 7th day,respectively.In the honey water treatment group,the survival time of male moths irradiated at 300 Gy and female moths irradiated at 150 Gy was 25 days,which was longer than that of the control male moths and female moths,which were 21 and 23 days,respectively.This indicates that the post-irradiation starvation tolerance of male and female moths is superior to that of the control group.Female pupae of S.frugiperda were irradiated with 150,50,and 10 Gy,and male pupae were treated with 300,50,and 10 Gy.The emergence rates of cylindrical flight were gradually decreased with the increasing dose of radiation,and the S.frugiperda treated with lower doses,such as 10 Gy,delayed the decrease in adult survival rate,with a lifespan of up to 28 days.These results show that there was no significant difference in starvation tolerance and flight ability between irradiated and control male and female S.frugiperda,which meet the requirements for release into the field.4.Assessment of sexual attraction response and mating ability on released population of ⁶⁰Co irradiated S.frugiperdaThe irradiation doses were set at 300 and 50 Gy,non-irridiated male pupae as control.The male and female moths were observed at 0:00 am,4:00 am,8:00 am,12:00 pm,16:00pm,and 20:00 pm,every day within 6 days after mating.The results of the sexual response test showed that the maximum percentage of males approaching females treated with 300Gy was 21.1%,44.5%,50%,50%,33.3%,and 28.6%,respectively,while the control group was 26.3%,38.1%,37.5%,41.1%,30%,and 33.3%,respectively.The percentage of the control group at the other 5 time points was lower than that of the 300 Gy irradiation group.The results of males treated with 300 Gy and 50 Gy were similar.Except at 12:00pm,the percentages of males treated with 50 Gy were lower than those treated with 300Gy,but higher than those of the control group.By observing the changes of the probability position of male S.frugiperda in the main and lateral arms with time,it was found that it was consistent with the results of the maximum percentage of male S.frugiperda close to that of female S.frugiperda.The maximum values of the males on the main arm treated with 300 Gy were 388.5,778.5,750,750,499.5,and 610.5 cm,respectively.The control group was 531,643.5,562.5,646,525 and 500 cm,respectively.Except at 0:00 am and16:00 pm,the maximum values of the control group on the main arm at the other 4 time points were lower than those of the male treated with 300 Gy.Indicating that the sexual attraction of female S.frugiperda to males treated with 300 Gy irradiation dose was stronger than that of males treated with 50 Gy irradiation and control males.Observing the number of sperm packages in the female to evaluate S.frugiperda mating ability,it was found that when S.frugiperda male were irradiated with a higher dose of radiation such as 300 Gy and mated with non-irradiated female moths,the number of sperm packages in the female moth’s body was significantly lower at 0.125 compared to the control group’s 1.38,indicating a decrease in mating ability with higher radiation doses.The overall experiment shows that using 300 Gy as the sterilization dose for irradiating S.frugiperda male moths is feasible.