Effects of Aging, Temperature and Photoperiod on Testis Development of Polygonia c-aureum (Lepidoptera : Nymphalidae)

The effects of aging, photoperiod and temperature on testis development in the Asian comma butterfly Polygonia c-aureum were examined in connection with adult diapause and overwintering. Photoperiods during larval, pupal and imaginal stages did not exert pronounced influences on testis development, indicating that testis development is not influenced by diapause (i.e. controlled photoperiodically). Larval testes size increased with time until the end of the pupal stage, and thereafter began to decrease, especially during the first month of adulthood. When adults were kept under short day length (SD) and three different temperatures (15℃, 21℃ or 25℃) after adult eclosion, the rate of testis shrinkage was lowest at 15℃. Irrespective of timing (15 or 45 days of adult age) and duration (1, 2 or 3 months) of chilling at 5℃, the size of shrunken testis remained nearly constant throughout the post-chilling period at 21℃. Field examination also showed that testis size after overwintering as well as in late autumn before overwintering remained small. These results suggest that testis shrinkage ceases before or during overwintering. After ecdysed to the final (fifth) larval instar, a yellow membrane covered the testes and began to degenerate at the end of the pupal stage. The timing of yellow membrane degeneration coincided with the commencing of testis shrinkage, apyrene sperm movement from testis to post-testicular organs, and reduction of apyrene spermiogenesis. Therefore, it is suggested that there is a distinct possibility of the yellow membrane being involved in these reproductive events of the testis.