Ecogenetical Studies on geographical variation and gene expression of diapause in the cotton bollworm, Helicoverpa armigera.

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The pupal diapause of the cotton bollworm, Helicoverpa armigera, was investigated. The results obtained are summarized as follows.1.Photoperiodic response of pupal diapause was investigated at lower temperature of 18℃. The diapause was induced under short day length conditions and its tendency was greater in males.2.The diapause induction under seminatural conditions was compared between H.armigera and H.Assulta. In H.armigera, some individuals could overwinter as diapausing pupae, although many individuals died before pupation with advance in the fall season. On the other hand, in H.assulta, pupal diapause was induced even at high temperatures in summer season. These results indicated that the adaptation to temperate climate is inadequate in H.armigera.3.No clear geographical cline in diapause tendency was detected It was supposed that pupal diapause is induced when larvae were exposed to lower temperatureds for a long time in fall season of subtropical region.4.It was estimated that the sensitive stage to day-length in pupal diapause is the 5th instar.5.Only the diapausing pupae are supposed to overwinter in the region where average winter temperatures are higher than 0℃. The trehalose was seemed to be responsible for the cold hardiness.6.It was indicated that nonadditive interactions among multiple loci are influential on the diapause rate. Moreover, it was found that there is a genetic correlation between larval period and diapause.From these results, it was concluded that H.armigera is fully possible to spread its distribution and increase its abundance in Japan with progress in the global warming.