Appraisal of Sperm Dynamics as a Crucial Trait of RadiosterilizedSpodoptera litura(Lepidoptera: Noctuidae) and Its F₁Progeny for Evaluation of the ‘Inherited Sterility Technique’ for Pest Suppression

Abstract

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.

Differential Apyrene Sperm Activation Elicited by Regions of Male Reproductive System of Spodoptera litura (F.)

“…The involvement of various regions of male reproductive system was ascertained towards apyrene sperm activation in S. litura by the sperm activation bioassay (as per method described by Seth et al, 2016a). The presence of sperm activator biomolecules in the prostatic part of S. litura has been reported earlier by Seth et al (2016a), whereas in the present study the male accessory glands secretions were also found to reinforce the sperm activity. Stephens et al (2018) reported the presence of trypsin like protease in the male accessory gland of Culex pipiens and Culex quinquefasciatus.…”

“…In lepidopterans, the males produce two distinct types of sperm-nucleated eupyrene and non-nucleated apyrene sperms. Spodoptera litura is a noctuid moth and is reported to exhibit sperm polymorphism (Seth et al, 2016a). The apyrene sperm of S. litura generally comprise about 75% of the sperm in the ejaculate (Seth et al, 2016b).…”

Effect of X-ray irradiation on development, flight, and reproduction of Spodoptera litura

“…Lepidopteran insects are more resistant to radiation than insects in other orders ( LaChance et al, 1975 ) because, after irradiation, the shattered chromosomal fragments attach to the centromere and are passed to the next generation through germ cells ( Proverbs and Newton, 1962 ; Marec and Traut, 1993 ). As a result, using substerile doses to irradiate insects can not only inhibit the development of parental populations but also reduce the number of their offspring ( Seth et al, 1997 ; 2016a ). This inherited sterility has provided remarkable advancement in the control of lepidopteran pests, such as Trichoplusia ni and Helicoverpa zea ( North and Holt, 1969 ; Carpenter and Gross, 1993 ).…”

Assessing the Radiation Hormesis on the Reproductive Behaviour of Male <i>Spodoptera litura</i> (F.) Treated with Low Dose Ionizing Radiation in the Pre-imaginal Stages

“…The adult male exposed to LDIR at preimaginal stages were used for the sperm activation assay. An invitro sperm bioassay was performed by the procedure described by Seth et al 2016 to assess the effect of LDIR on sperm motility. Sperm and activator were produced as described below for the in-vitro sperm assay.…”

“…Apyrene sperms, on the other hand, play a role in sperm competition and proper functioning of eupyrene sperm (Silberglied et al, 1984;Gage and Cook, 1995). Sperm dynamics is considered as a crucial factor for insect's viability and mating competitiveness (Seth et al, 2016). Hence, it is important to maintain a reasonable level of the life span, insemination quality and mating competitiveness of the irradiated pest moths that would be employed in F1 sterility technique for pest suppression.…”