Seasonal and altitudinal adaptations in three katydid species:ecological significance of initial diapause

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  • Seasonal and altitudinal adaptations in three katydid species ecological significance of initial diapause

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Abstract

The life cycle and diapause characteristics were compared among three katydid species to investigate the ecological function of initial diapause in katydids. Metrioptera japonica (Bolivar) inhabiting northern areas as well as alpine regions of its southern range required two or more years to complete its life cycle and showed two types of embryonic diapause : one occurs just after blastoderm formation (initial diapause) and the other shortly before hatching (final diapause). Some eggs of this species remained in initial diapause for several years. Initial diapause was terminated at 25℃ after chilling at 3℃ for six months, but the rate of termination was lower in eggs derived from higher altitudes. Metrioptera hime Furukawa and Chizuella bonneti (Bolivar) are univoltine and entered diapause only at a late embryonic stage. These univoltine species hatched over a relatively long period of time in spring but emerged as adults by summer, because they occur only at lowlands. The time of adult emergence in M. japonica at high altitudes varied greatly from year to year, and adults appeared relatively late in the season. Because eggs of this species survived a period of chilling even before reaching the initial diapause stage, initial diapause is probably not a prerequisite for overwintering. Variation in the time of oviposition or induction of initial diapause did not affect the timing of hatching that occurred two years later. It appears that in M. japonica initial diapause plays an important role in the control of the life cycle in habitats where the growing season is short and unpredictable.

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