The eupyrene-apyrene dichotomous spermatogenesis of Lepidoptera. The relationship with postembryonic development and the role of the decline in juvenile hormone titer toward pupation.

The relationships between the stages of postembryonic development and the occurrence of eupyrene and apyrene spermatogenesis, and the effects of the decline of the juvenile hormone (J.H.) titer toward pupation in these processes, were studied in the carob moth, Ectomyelois ceratoniae. The accurate timing of the spermatogenetic events was determined daily from the 2nd instar larva to the imago in squashes and electron microscope preparations of testes. Eupyrene spermatids elongate in two phases. In the first, beginning in late 4th instar larva, only flagella elongate, while in the second, beginning in the mid 5th instar larva, both flagella and nuclei elongate. Apyrene spermatogenesis starts just after the beginning of the nuclear elongation of eupyrene spermatids, in the mid 5th instar larva and not in the pupa, as is commonly believed. Using ligatures, topical applications of a J.H. mimic, and testes transplantation, it was found that the nuclear elongation begins in the 5-day-old eupyrene spermatid and cannot be induced earlier; the elongation is inhibited by high titer of the J.H. mimic. Elongation of the flagella, however, is unaffected by fluctuations of the J.H. titer. The onset of the apyrene spermatogenesis, which occurs in the very early 5th instar larva or before, was found to be unrelated to the decline in the J.H. titer toward pupation.