Effects of gamma irradiation on the mechanisms of sperm transfer in Trichoplusia ni

Abstract

The mechanisms involved in the transfer of sperm by unirradiated and irradiated cabbage loopers were studied by live dissection of the female immediately after the initiation of mating. This technique allows for observation of the entire mating and sperm transfer process. Failure of gamma-sterilized (30 krad.) adult male cabbage loopers to transfer sperm to the spermatheca was due to the inability of the irradiated males properly to incorporate sperm into the spermatophore bulb. The time required for mating was significantly longer for gamma-sterilized male moths. The timing of the insertion of the spermatophore, inflating the spermatophore bulb, and the inclusion of sperm into the bulb was altered in irradiated moths. Most irradiated males studied everted their endophallus early and ejaculated into the bursa copulatrix. Since eupyrene sperm have no motility until reaching the spermatheca, they have no way of being utilized for fertilization. A fraction of the apyrene sperm, on the other hand, find their way from the bursa copulatrix to the spermatheca since this type of sperm is motile at the time of ejaculation. Apyrene sperm being anucleate cannot effect fertilization so that radio-sterilization of the cabbage looper is essentially due to lack of sperm utilizable by the female. Irradiated males ejaculated the same number of eupyrene and apyrene bundles as the controls. These studies indicate that the elicitation of the ovipositional response is initiated by one or more of the male accessory secretions which must be incorporated into the spermatophore bulb to be effective.