Abstract
In warm temperate and subtropical regions an adult summer diapause regulates the timing of oviposition. Epilachna admirabilis is a univoltine phytophagous lady beetle ranging from south to north Japan, Taiwan, China and Myanmar. In Japan the species hibernates in the full-grown larval stage. In cool temperate Sapporo (43°04´N) the adults never enter summer diapause but pass a second winter in diapause. This study revealed that in Kyoto (35°01´N), the adults had a summer diapause induced by an intermediate photoperiodic response; they had a critical photoperiod of approximately 14.5 h light per day. All females entered reproductive diapause under a long photoperiod of 16L (light) : 8D (dark) and 6.7% of them did so under shorter photoperiods of 13L : 11D and 12L : 12D. However, diapause incidence was 40% at 8L : 16D, suggesting the existence of a second critical photope- riod at a photophase slightly less than 8 h. At photophases of 12-15 h, non-diapausing females laid eggs on average between 27.1 to 39.0 days after emergence. Photoperiod reversibly regulated the induction, maintenance and termination of the adult diapause. Tem- peratures of 20-30°C did not affect the incidence and termination of diapause at 16L : 8D. Adult winter diapause at the higher lati- tude Sapporo might have originated from adult summer diapause at middle latitude regions such as Kyoto. Selection at increasing latitudes would have forced northerly populations of the species to lose the adult summer diapause in the range of natural day- lengths. Subsequent selection pressure should have favored adults that avoided futile oviposition in late summer or autumn, survived cold winters in diapause and commenced an additional oviposition in the second summer. Thus, a latitudinal difference in photoperi- odic responses might have developed.
Highlights
Diapause halts or delays development of insects at specific developmental stages, and enables synchronisation of life cycles to season (Danilevskii, 1961; Tauber & Tauber, 1976; Danks, 1987)
In the lady beetles of genus Epilachna, ovarian diapause is induced by short day-length in E. vigintioctomaculata (Maki et al, 1964), E. vigintioctopunctata (Kono, 1986) and E. varivestis (Taylor & Schrader, 1984) as well as the cool temperate Sapporo population of E. admirabilis (Hoshikawa, 2000)
Females that did not lay any eggs within 70 days were considered to have entered a reproductive diapause
Summary
Diapause halts or delays development of insects at specific developmental stages, and enables synchronisation of life cycles to season (Danilevskii, 1961; Tauber & Tauber, 1976; Danks, 1987). Diapause in the adult stage regulates the timing of oviposition of many species (Danilevskii, 1961; Masaki, 1980; Danks, 1987). Adult winter diapause has been reported in many species of long-day insect (Danilevskii, 1961; Tauber & Tauber, 1976; Danks, 1987) including most Coccinellidae species (Hodek, 1996). In the lady beetles of genus Epilachna, ovarian diapause is induced by short day-length in E. vigintioctomaculata (Maki et al, 1964), E. vigintioctopunctata (Kono, 1986) and E. varivestis (Taylor & Schrader, 1984) as well as the cool temperate Sapporo population of E. admirabilis (Hoshikawa, 2000). The ten-spotted lady beetle E. admirabilis Crotch is a univoltine species feeding on wild cucurbits such as Gynostemma pentaphyllum, Trichosanthes cucumeroides, T. kirilowii and Schizopepon bryoniaefolius. In contrast to most Coccinellidae species, E. admirabilis hibernates as a fullgrown larva in warm
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