Spermatogenesis of the Southwestern Corn Borer, Diatraea grandiosella. 2. Resumption in Diapause Larvae1,2

Abstract

Spermatogenesis was examined during the mature larval diapause of the Diatraca grandiosella Dyar. Diapause larvae were exposed to 3 environmental regimes, 30°C 24L:0D, 30°C 12L:12D, and 23°C 12L:12D, to vary the rate of diapause development. Results showed that during the 1st phase of diapause development the testes became yellow and shrunken, spermatogenesis was arrested, and secondary spermatocytes degenerated. Degeneration was completed within 20 days in larvae held at 23°C 12L:12D and in 60 days in those held at 30°C 12L:12D. Primary spermatocytes in the pachytene stage of meiosis were the most mature stage of the germ cells which remained. A resumption of spermatogenesis occurred during the last phase of diapause development. Follicles containing germ cells in all stages of differentiation were found before the larvae entered the postdiapause pupal molting cycle. A similar arrestment and resumption of spermatogenesis was found during diapause development of field-collected larvae. The effect of 20-hydroxyecdysone on spermatogenesis was examined using 63-day-old diapause larvae which had been exposed to a regime of 30°C 24L:OD for 24 days. Results showed that within 42 hours of treatment differentiation of the germ cells resumed, and secondary spermatocytes were present. This finding suggests that ecdysone is secreted at a low titer during the last phase of diapause development. This titer is apparently sufficient to cause resumption of spermatogenesis but inadequate to initiate the pupal molting cycle.