GEOGRAPHIC-VARIATION IN PHOTOPERIODIC RESPONSES IN AN INTRODUCED INSECT, HYPHANTRIA-CUNEA DRURY (LEPIDOPTERA, ARCTIIDAE) IN JAPAN

Photoperiodic responses for diapause induction and post-embryonic development were investigated in six geographic populations of an introduced insect, Hyphantria cunea DRURY in Japan. Incidences of diapause varied among populations under 14.5L-9.5D at 20-degrees-C. Estimates of critical photoperiods fell between 14 hr 23 min and 14 hr 43 min. Those for the northern populations were not critically different from the original population which initially colonized. However, those for the southern trivoltine populations were shorter than those for the northern bivoltine ones. The critical photoperiods were nearly the same within each voltinism region. The period for larvae not destined to diapause was generally shorter than the one for diapause-destined larvae. This tendency was more conspicuous in the trivoltine populations. The non-diapause-destined larval and pupal periods in the trivoltine Kobe population were shorter than those in the bivoltine ones under 16L-8D at 20-degrees-C. Under 14L-10D at 20-degrees-C, however, the diapause-destined larval period in the Kobe population was not different from the larval periods in all but one bivoltine population. Voltinism, critical photoperiod for diapause induction and developmental period of this species have changed during its 40-year colonization of Japan.