Influence of parasitism on spermatogenesis in the codling moth, Cydia pomonella L.

Abstract

Under laboratory conditions codling moth larvae ( Cydia pomonella L.) parasitized late in their embryonic stage contained both testes and an endoparasitoid larva ( Ascogaster quadridentata Wesmael); this allowed synchronous observations of both parasitoid larval development and spermatogenesis. Spermatogenesis up to the diffuse stage was identical in both the late-parasitized and healthy males at the beginning of the fourth stadium. Two days into the fourth stadium, parasitized individuals initiated precocious wandering and cocoon spinning activity, and the parasitoid larva molted into its second instar, while healthy codling moth larvae molted to their fifth instar. The second instar parasitoid larva grew rapidly and reached its maximum volume within 2 or 3 days. Spermatogenetic cells in a host with a late second stadium parasitoid initiated rapid development, early eupyrene spermatids were common and some elongation of eupyrene spermatids were observed before the third instar parasitoid egressed and consumed the entire host as an ectoparasitoid. Other host eggs, after delayed exposure to parasitoid attack, were chilled which resulted in pseudoparasitized hosts containing testes. This condition allowed us to observe spermatogenesis in fourth stadium codling moth without the parasitoid larva consuming the host. The timetable of spermatogenesis in pseudoparasitized individuals corresponded to that observed in late-parasitized larvae, but in addition to numerous eupyrene spermatids with elongating nuclei, apyrene metaphases and apyrene spermatids were observed. Precocious reprogramming of spermatogenetic cells occurs in the fourth stadia of both late-parasitized and pseudoparasitized hosts. Premetamorphic host wandering, cocoon spinning activity and presumably endocrine changes associated with this behavior caused both the testes to initiate spermatogenesis and the parasitoid larva to molt to second stadium. When both the parasitoid larva and testes shared host ecdysteroids, spermatocytes degenerated and primary spermatocytes lysed, similar to the situation found in healthy males destined to enter diapause. In pseudoparasitized males, where testes were the sole recipient of ecdysteroids released at the time of wandering, spermatogenesis continued to where both eupyrene and apyrene spermatids were formed, a condition representative of an impending larval pupal molt .