Seasonal life cycles and resource uses of flower-and fruit-feeding drosophilids (Diptera, Drosophilidae) were studied at low to high altitudes in central Japan to understand their adaptation to seasonal changes of environmental conditions. Drosophila unipectinata 3

Abstract. 1. In central Japan, Drosophila curviceps Okada and Kurokawa was collected in spring and autumn but not in summer at lowlands (alt. 500–1200 m), while it was collected only in summer at highlands (1500–2000 m). Experiments on its thermal tolerance suggested that summer heat at the lowlands and winter low temperatures at the highlands were adverse to this species. It is considered that this species escapes from these extreme temperatures by undergoing seasonal migration between the lowlands and the highlands. This species had no photo‐periodic diapause and bred at both lowlands and highlands. 2. D.immigrans Sturtevant was less cold‐hardy but more heat‐tolerant than D.curviceps. It is considered that this species is unable to overwinter outdoors at least in the study areas (i.e. alt. 500m or higher in central Japan) and its populations in these areas originate with migrants from warmer areas. 3. D.albomicans Duda, a subtropical species, was less cold‐hardy but more heat‐tolerant than the above two species. 4. Climatic adaptations and distributions of these species are discussed with reference to their thermal tolerance.

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The phylogenetic relationship of Eurasian species of the Drosophila obscura species group remains ambiguous in spite of intensive analyses based on morphology, allozymes and DNA sequences. The present analysis based on sequence data for cytochrome oxidase subunit I (COI) and a-glycerophosphate dehydrogenase (Gpdh) suggests that the phylogenetic position of D. alpina is also ambiguous. These ambiguities have been considered to be attributable to rapid phyletic radiation in this group at an early stage of its evolution. Overwintering strategies are diversified among these species: D. alpina and D. subsilvestris pass the winter in pupal diapause, D. bfisciata and D. obscura in reproductive diapause, and D. subobscura and D. guanche without entering diapause. This diversity may also suggest rapid radiation at an early phase of adaptations to temperate climates. O n the other hand, adult tolerance of cold was closely related to overwintering strategy and distribution: D. obscura and D. bfmciata with reproductive diapause were very tolerant; D. alpina and D. subsilvestris which pass the winter in pupal diapause were less tolerant; D. subobscura having no diapause was moderately tolerant and D. guanche occurring in the Canary Islands was rather susceptible. Tolerance of high temperature at the preimaginal stages seemed to be also associated with overwintering strategy; i.e. lower in the species with pupal diapause than in those with reproductive diapause or without diapause mechanism. 0 1999 The Linnean Society of London ADDITIONAL KEY WORDS:-diapausemolecular phylogeny ~ temperature tolerance.

Drosophila moriwakii Okada & Kurokawa (Diptera; Drosophilidae) generally has only one generation per year and enters aestivo‐hibernal reproductive diapause in Sapporo, northern Japan, but a small fraction of the population produced a second generation in summer at a place where breeding resources were abundant. In this species, diapause seems to be controlled by flight activity. When flies were cultured in cages in which they were able to fly freely, they entered diapause irrespective of photoperiod, but they did not do so at long daylengths when cultured in small vials in which they were prevented from flying. Furthermore, flies with wings removed did not enter diapause at long daylengths even if they were cultured in the cages.