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.

Mass rearing of insects of high biological quality is a crucial attribute for the successful implementation of sterile insect release programs. Various ontogenetic stages of Spodoptera litura (Fabr.) were treated with a range of low doses of ionizing radiation (0.25–1.25 Gy) to assess whether these gamma doses could elicit a stimulating effect on the growth and viability of developing moths. Doses in the range of 0.75 Gy to 1.0 Gy administered to eggs positively influenced pupal weight, adult emergence, and growth index, with a faster developmental period. The enhanced longevity of adults derived from eggs treated with 0.75 Gy and 1.0 Gy, and for larvae and pupae treated with 1.0 Gy, indicated a hormetic effect on these life stages. Furthermore, the use of these hormetic doses upregulated the relative mRNA expression of genes associated with longevity (foxo, sirtuin 2 like/sirt1, atg8) and viability/antioxidative function (cat and sod), suggesting a positive hormetic effect at the transcriptional level. These results indicated the potential use of low dose irradiation (0.75–1 Gy) on preimaginal stages as hormetic doses to improve the quality of the reared moths. This might increase the efficiency of the inherited sterility technique for the management of these lepidopteran pests.

In this study various factors, viz., male irradiation, its mating status and post mating interval were studied on the remating propensity, insemination quality and reproductive behaviour of a noctuid pest Spodoptera litura (F.) that may govern the efficacy of radiation mediated inherited sterility (IS) technique proposed to control this pest. The male irradiation (substerilizing 130 Gy and sterilizing 250 Gy) affected the copulation duration, mating success and sperm transfer during mating. Multiple matings of male significantly depleted the sperm in fully sterile male followed by substerile male than control. During remating with virgin female, the reproductive performance of mated irradiated male, was more affected at 24 hr than at 48 hr inter mating interval, which might be due to associated physiological impact on mating behaviour and insemination quality. This study might be crucial in simulation modelling and optimization of successful implementation of IS programme.

The ‘Inherited or F1 sterility technique’ (IS), using sub-sterilized male moths, is a widely proposed pest management tool for Lepidoptera pests in general, and the tobacco cutworm Spodoptera litura (Fabr.) in particular. However, the multiple mating tendency of female moths and the ejaculate quality of male moths might influence the efficiency of this technique. Reduced ejaculate quality was observed in irradiated males, as evidenced by radiation’s impact on certain bio-parameters, such as the weight of the spermatophores and their protein content, sperm count, the molecular expression of the sex peptide receptor (SPR) and egg fertility, with a greater impact in F1 male progeny. During the remating of females with untreated males, irrespective of the irradiation status of the first male, there was an increase in calling behavior, remating propensity and fertility in females, with a larger time gap between consecutive matings. The ability of F1 male progeny to check remating propensity in females 24 h after the initial mating was lower than that of unirradiated males. Partially sterile (130 Gy) males were as successful as unirradiated males in inducing the level of mating refractoriness in females. Decreased ejaculate quality in F1 male progeny could be associated with increased female receptivity during remating. Understanding the influence of male moth irradiation, insemination quality and post (initial)-mating intervals on the remating behavior of normal female moths and induced sterility might help in simulation modeling and optimizing IS insect programs.

In this study, the effect of ionizing radiation was studied on the pheromone biosynthesis activating neuropeptide (PBAN) gene expression in female moths of a noctuid pest Spodoptera litura (F.), that would trigger pheromone production and its release needed for calling behaviour. The PBAN gene expression in the radiosterilized female moths (at 130 Gy) showed a decline with respect to control (unirradiated moths), and PBAN expression was drastically reduced at higher dose, 200 Gy. The photosensitivity and diel rhythm of PBAN gene expression, indicating higher expression during peak hours of scotophase and lowest expression during photophase was maintained at 130Gy, which deemed this gamma dose a suitable sterilizing dose for female moths which seemed to retain reproductive competence. This study might support the radiosterilized female moths for their combined release with substerilized males, using 130Gy to effectively operate the F1 sterility technique proposed to control S. litura