Developmental Differences on the Internal Reproductive Systems between the Prediapause and Prereproductive Riptortus pedestris Adults

Riptortus pedestris (Heteroptera: Alydidae), an important crop pest, is capable of entering reproductive adult diapause under short-day photoperiods. Though the physiological aspects of adult diapause have been well studied in this species, little is known about its morphological development. In the present study, the adult females are discriminated as prediapause and prereproductive based on the absence and presence of mature oocytes in ovarioles, respectively. We also measured the morphological development of vitellarium and lateral oviduct in females, and the accessory gland, ejaculatory duct, and testes in males of both prereproductive and prediapause adults. Our results revealed that there is a clear significant difference in the reproductive development of prediapause and prereproductive insects. Moreover, the internal morphology of reproductive organs was suppressed in prediapausebugs compared to prereproductive bugs, and the insects developedthe reproductive parts as newly emerged adults. The above findings provide basic knowledge on the characterization of diapause and reproductive R. pedestris adults, which would be applicable to molecular investigations.

Experimental Evidence Supporting an Obligate Adult Diapause for Spruce Beetle (Coleoptera: Curculionidae) from British Columbia

Insects respond to environmental conditions with a variety of developmental responses which include changing developmental rates, or suppressing development altogether in quiescence or diapause. Such responses have important implications for survival and voltinism. The spruce beetle, Dendroctonus rufipennis Kirby (Coleoptera: Curculionidae), has long been assumed to have an obligatory adult diapause based on field observations that adults always overwinter prior to dispersing and reproducing; however, it has never been experimentally demonstrated and recent evidence suggests that adults in some populations may exhibit facultative tendencies. We examined the emergence of adults at a constant 22°C after exposure to 2°C for 0 (no cold), 25, 50, and 75 d. Our observations of a delayed and extremely protracted emergence period in the absence of a substantive cold period, which could last several months, in combination with rapid, synchronous mass emergence after a substantive cold period, are most consistent with an obligate diapause. Approximately 50% of individuals could complete diapause in 55 d at 2°C, and 75 d of cold was adequate for almost all individuals to complete diapause. Beetles that emerged slowly over time may still have been in diapause; however, additional research would be required to test this hypothesis. Conditions throughout the beetle’s range in Canada should facilitate successful completion of diapause. An obligate adult diapause for spruce beetle populations in western Canada would limit the shortest possible life cycle to 1 yr, but would also serve to maintain an adaptive 1-yr life cycle, especially under a changing climate.

Field and Laboratory Studies on the Ecology, Reproduction, and Adult Diapause of the Asian Comma Butterfly, Polygonia c-aureum L. (Lepidoptera: Nymphalidae)

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.