Irradiation impact on stress-indicating molecular responses in F1 progeny is correlated with its reproductive performance. These observations will permit defining regimen having pragmatic viability of 'F1 sterility technique' for pest suppression. Gamma dose of 100 Gy would ensure balance between induced sterility of males and their field competitiveness. These parameters would facilitate integration of biocontrol strategy with parabiological 'Sterile Insect Release Technique'.

The dose of radiation applied to the Oriental leafworm (also known as the common cutworm), Spodoptera litura (F.) (Lepidoptera: Noctuidae) for use in inherited sterility (IS) sterility programs must not materially reduce the quality and competitiveness of the released males. To assess the quality of sub-sterilized male moths and their F 1 progeny, their flight and mating behaviors were investigated. Thus, parental (P) generation S. litura males that had been irradiated with either 100 or 130 Gy and their F 1 male descendants were subjected to flight assay tests to assess flight ability, orientation towards a pheromone source and mating behavior, i.e., mating performance using various sex ratios, sequential matings, and effect of female age. The orientation behavior of either P or F 1 males towards pheromone-baited traps was not different from that of non-irradiated males. Mating abilities of irradiated P generation males and their F 1 male progeny with non-irradiated females were studied using several sex ratios, but large differences were not found even when the sex ratio was increased from 1:1 to 5:1. A study on sperm use patterns revealed the precedence of sperm of the last male to mate, for example, when a non-irradiated female was sequentially mated with a non-irradiated P male, followed by an irradiated P male and finally by an F 1 male, as well as in all other possible sequences of such males. Mating success, remating propensity and fertility were significantly influenced by mating sequences that included irradiated males. Further, the age of the female at the first mating influenced fertility in matings with F 1 males, and mating success and remating propensity were reduced in several of sequences of matings involving non-irradiated and irradiated males and F 1 males, with reductions being more apparent when females were aged 5-6 d. The present study indicates that gamma doses of either 100 or 130 Gy are suitable for the suppression of S. litura using an IS approach.

The present study was conducted to appraise the ontogenic radio-sensitivity of a serious tropical pest, Spodoptera litura (Fabr.). The molecular responses pertaining to the phenoloxidase (PO) pathway and an anti-oxidant defense mechanism were evaluated in order to understand its implication in pest control at pre-harvest and post-harvest intervals. Irradiation exhibited an inverse relationship with age with respect to impact on developmental and transcriptional responses. Transcript abundance of PO cascade enzymes, prophenoloxidase (slppo-2), its activating enzyme (slppae-1) and free-radical scavenging enzymes, superoxide dismutase (slsod) and catalase (slcat) was evaluated upon gamma irradiation alone and the dual-stress of radiation plus microbial challenge. The slppo-2, slppae-1, slsod and slcat transcripts were significantly up-regulated in F 1 L6 larvae (6th-instar) resulting from 100 Gy sub-sterilized male adults and unirradiated female moths. The extent of upregulation was relatively higher in comparison with L6 survivors (6th-instar larvae) developed from irradiated neonates (L1) treated with 100 Gy. Upon Photorhabdus challenge, the transcripts were down-regulated in irradiated L1 suggesting increased larval susceptibility to bacterial infections. Radioresistance increased with the age of the insect, and molecular responses (transcript abundance) of insect defense mechanism were less influenced when older age (F 1 progeny) were irradiated. These findings will help to optimize the gamma dose to be employed in inherited sterility technique for (pre-harvest) pest suppression and (post-harvest) phytosanitation and quarantine, and suggest compatible integration of biorational tactics including nuclear technology.

Sperm behavior represents one of the attributes in the radiogenetic technique called inherited sterility crucial for its effectiveness to suppress populations of Spodoptera litura (F.) (Lepidoptera: Noctuidae). Quantitative and qualitative assessments of S. litura sperm behavior (production, descent, activation, movement and transfer to females) were made in parental (P) males that received sub-sterilizing irradiation doses of either 100 or 130 Gy and in their F 1 generation males. Age dependent production of eupyrene and apyrene spermatozoa in the testes were not affected by such irradiation in the P males, nonetheless a slight but significant effect occurred in the F 1 generation. During the rhythmic cycles of sperm descent in the photophase and scotophase, the profile and proportion of sperm descent from the testes to the upper vas deferens (UVD), seminal vesicle (SV) and duplex were not significantly influenced by irradiation in P and F 1 males. Sperm activation-assessed as percent active apyrene sperm and their intensity of motility-was not diminished in irradiated P males, while in F 1 males it showed a slight but significant reduction. Mating status was not a markedly pronounced factor in eliciting the motility of irradiated sperm. Sub-sterilized P males and their F 1 progeny were nearly as competitive as non-irradiated males in terms of sperm transfer from male to female. Successful amphimixis occurred between the altered genomes of either irradiated P males or F 1 males and the non-irradiated female genome; consequently dose dependent reductions in percent egg hatch were observed in the hatching of F 1 and F 2 eggs. Irradiation with either 100 or 130 Gy did not adversely influence the sperm characteristics in the irradiated P males and their F 1 male progeny, and this study validated the sperm' viability and performance in irradiated P males and of their F 1 sons. The findings indicated that these genetically altered sperm would fertilize the eggs of wild females and lead to effective control of this tropical pest.

The present study suggests that Lepidopteran insect cells carry a stronger antioxidant system that protects against radiation-induced macromolecular damage, growth inhibition and cell death.