Effect of Irradiation on Reproduction of Female ISpodoptera litura/I in Relation to the Inherited Sterility Technique

Spodoptera litura (Fabr.) is a serious Lepidopteran pest that can be controlled using the eco-friendly radio-genetic Inherited (F1) Sterility (IS) technique. In contrast with the conventional male-only release applied in IS techniques, this study was conducted to determine a suitable dose at which females can be fully radio-sterilized while leaving the more radio-resistant males partially sterile, meaning that both sexes could be irradiated together and released simultaneously in pest infested fields. Behavioral and molecular investigations ascertained 130 Gy to be a suitable dose for female sterilization, at which point their reproductive fitness in terms of calling ability and mating competence will not be significantly compromised. These irradiated females would be sufficiently viable to compete with wild females for mating with wild males, ultimately suppressing the pest population. The simultaneous release of sub-sterile male and sterile female moths using the IS technique might improve its efficacy, leading to more effective pest suppression. Radiobiological investigations on the reproductive behavior of female Spodoptera litura (Fabr.) were conducted with the aim of determining the suitable radio-sterilizing dose for females in order to release them along with sub-sterile males for effective implementation of the Inherited Sterility technique against this pest. Calling and copulation duration significantly increased, while mating success, oviposition, fertility and longevity significantly decreased with increasing radiation dose (100–200 Gy) compared to control. In view of the effect of irradiation on mating behavior and reproductive viability of female S. litura, 130 Gy was identified as a suitable radio-sterilization dose. Further molecular studies were conducted to corroborate this dose for female sterilization, along with a higher dose of 200 Gy in order to validate the gradational response of ionizing radiation. GC-MS analysis indicated decreased sex pheromone titer at 130 Gy, which was more pronounced at 200 Gy. Pheromone-associated genes, PBAN and PBAN-R showed decreased expression at 130 Gy, and were drastically reduced at 200 Gy. The fertility-related Vg gene also showed a negative correlation with radiation exposure. Based on these radiation responses of female S. litura, 130 Gy might be considered a suitable dose for complete female sterility and its inclusion in sterile insect programs against S. litura.