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We investigated the effects of juvenile hormone analogue (methoprene) and 20-hydroxyecdysone on female and male reproduction in a nymphalid butterfly, Polygonia c-aureum. This butterfly has a facultative adult diapause controlled by the corpora allata and brain. Methoprene seems to terminate reproductive diapause, although transplantation experiments indicate that the activity of the corpora allata does not affect male mating behavior Endo (Dev Growth Differ 15:1-10, 1973a), suggesting that the brain may be involved in diapause. We found that exposure to methoprene promoted the development of ovaries and of the male accessory glands and simplex. On the other hand, exposure to 20-hydroxyecdysone did not promote the development of female and male reproductive organs and eupyrene sperm movement from the testis to the duplex in the adult stage. Ecdysteroid titer in both sexes was consistently low in adults. These results suggest that imaginal diapause is largely regulated by juvenile hormone in this butterfly.

In general, sperm produced in the testis are moved into the seminal vesicle via the vas deferens in insects, where they are stored. How this sperm movement is controlled is less well understood in locusts or grasshoppers. In this study, the effects of age, phase variation and pheromones on male sperm storage were investigated in the desert locust, Schistocerca gregaria (Forskål). In this locust, a pair of ducts, the vasa deferentia, connect the testes to a pair of the long, slender seminal vesicles that are folded approximately thirty times, and where the sperm are stored. We found that phase variation affected the level of sperm storage in the seminal vesicle. Moreover, adult males that detected pheromones emitted by mature adult males showed enhanced sperm storage compared with males that received the pheromones emitted from nymphs: The former, adult male pheromones are known to promote sexual maturation of immature adults of both sexes, whereas the latter, nymphal pheromones delay sexual maturation. Most mature adult males had much sperm in the vasa deferentia at all times examined, suggesting daily sperm movement from the testes to the seminal vesicles via the vasa deferentia. As adult males aged, sperm were accumulated from the proximal part to the distal end of the seminal vesicle. Many sperm remained in the seminal vesicle after mating. These results suggest that young or new sperm located near the proximal part of the seminal vesicle could be used for mating, whereas old sperm not used for mating are stored in the distal part of the seminal vesicle.

The effects of temperature, photoperiod and aging on eupyrene sperm movement from the testis to the duplex in Polygonia c-aureum male adults were examined in relation to seasonal form and imaginal diapause. In males of both summer and autumn forms obtained under long-day and short-day conditions, respectively, the number of eupyrene sperm bundles in the duplex increased linearly with age during the early stage of adult life at 21 degrees C, and no marked difference was observed between the two seasonal forms. Photoperiod during the adult stage did not influence the rate of sperm movement in autumn forms with diapause. The lower the temperature, the smaller the number of sperm bundles moved from the testis to the duplex. Sperm movement did not appear to occur during a period of chilling at 5 degrees C. Males of the autumn form which were pre-incubated for 30 days and chilled for 60 days failed to resume rapid sperm movement at the final incubation temperature of 21 degrees C. Those which were pre-incubated only for 15 days at 21 degrees C had much fewer sperm bundles in the duplex after chilling than those pre-incubated for 45 days. These results suggest the possibilities that eupyrene sperm movement is suppressed strongly during and after overwintering in the field, and that the eupyrene sperm to be used for reproduction in spring are transferred from the testis to the duplex before overwintering.

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Adult diapause and reproduction of a nymphalid butterfly, Polygonia c-aureum L., were investigated in field and laboratory examinations. Laboratory studies showed that old virgin male butterflies of non-diapausing generations had heavy accessory glands and simplex, which were suppressed in diapausing generations. The number of eupyrene sperm bundles in the duplex increased with adult age, whereas testis size decreased with age. Field examinations indicated that reproductive development of both sexes of diapausing generations in autumn was suppressed, and developed in spring. We attempted to estimate the physiological age of wild-caught males, as adult male age can be estimated from the testis size. We also attempted to determine whether or not wild male butterflies had mated from the development of the accessory glands and simplex, as well as the number of eupyrene sperm bundles in the duplex, by comparing unmated males with mated males. Field examinations suggest that almost all females in a population of non-diapausing generations mated and showed a tendency toward polyandry, while in the diapausing generation, in spring, monoandry rather than polyandry predominated. This suggests a different mating strategy between non-diapausing and diapausing generations.

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