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Acharya N G Ranga Agricultural University
The research work entitled “Studies on Effect of Gamma Radiation on Biological Parameters, Male Sterility and Bacterial Gut Symbionts of Fall armyworm, Spodoptera frugiperda (J.E. Smith)” was carried out at Insectary, Department of Entomology, S. V. Agricultural College, Tirupati and Plant Pathology laboratory, Citrus Research Station, YSRHU, Tirupati during 2021-22. The male pupae (7-8 days old) of Fall armyworm were exposed to eight different doses of gamma radiation (25, 50, 75, 100, 125, 150, 175 and 200 Gy) and studied the biological parameters viz., adult emergence, deformation, adult longevity and survival of irradiated males of parental generation. The effect of gamma radiation on F1 generation was also assessed by recording larval duration, pupal recovery, pupal weight, sex ratio, adult emergence, deformation, adult longevity and survival of F1 adults. Radiation doses; 25, 50, 75 and 100 Gy had not caused deleterious effects on biological parameters and quality of irradiated males of Fall armyworm. Among all doses (25 to 200 Gy) tested, radiation dose of 100 Gy had induced >80.00% of sterility with least negative effects on adult emergence (71.00%), deformation (9.00%), adult longevity (6 days) and survival under food stress (59.00%) in parental generation. Total developmental period of F1 larvae was 23.67 days at 100 Gy compared to 20.33 days at unirradiated control. Radiation doses from 25 to 100 Gy, larval period was prolonged by just 3 days only. More than 50% of pupae (51.33%) were recovered with pupal weight of 1.51 g/10 pupae at 100 Gy. Further increase in radiation doses from 125 to 200 Gy, larval duration was increased by 8 days (at 200 Gy), pupal recovery and their weight were significantly decreased as the radiation doses increased. The percentage of emergence of F1 adult at 100 Gy was 66.23% with least percentage of deformation (12.60%) and F1 adults lived up to 5.55 days with 52.00% of survival under food stress. But at radiation doses of 125 Gy onwards; adult emergence was declined with increased percentage of xiv deformation. Longevity and survival of F1 adult males were also severely affected at radiation doses ranging from 125-200 Gy. Optimization of gamma radiation dose was conducted to identify the radiation dose that could induces >80% of sterility without causing much negative impacts on the quality of sterile males. Percentage of male sterility was increased with increase in radiation doses. It was found that a radiation dose, 100 Gy has induced male sterility of 81.89% and 86.23% in parental and F1 generation of fall armyworm with no deleterious effects on adult emergence, longevity, survival and other quality parameters of sterile males. Although more than 90%of male sterility was recorded at radiation doses higher than 100 Gy (i.e. 125, 150, 175 and 200 Gy) but the quality parameters of sterile males of both parental generation and F1 generation were negatively affected. Therefore, a radiation dose of 100 Gy was identified as an optimum dose as it induced maximum male sterility without compromising with quality of sterile males. Bacterial gut symbionts from sterile (100 Gy), wild and lab reared males were isolated and identified based on 16s rRNA gene sequencing. Bacterial symbionts isolated from the guts of sterile males were identified as Staphylococcus hominis, Enterobacter hormaechei and Bacillus subtilis. Whereas the gut microbiome of unirradiated wild males were rich in Enterobacter hormaechei, Klebsiella variicola, Bacillus subtilis, Serratia marcescens, Staphylococcus hominis, Citrobacter sp. and Bacillus mojavensis. Bacterial symbionts obtained from lab reared males were Enterobacter hormaechei, Bacillus subtilis, Klebsiella sp. and Staphylococcus hominis. Microbial richness was apparently more in wild males followed by lab reared males and sterile males. The most dominant phylum of bacteria found among sterile, wild and lab reared males was Proteobacteria followed by the phylum Firmicutes. Among all the bacterial gut symbionts; Enterobacter hormaechei, Bacillus subtilis and Staphylococcus hominis were common bacterial symbionts in sterile, wild and lab reared males of Fall armyworm. Bacterial symbionts were less abundant in sterile males due to irradiation and they lost Klebsiella and Citrobacter in their guts