Effect of Population Density on the Larval Coloration and Development of Larva and Pupa in the Larger Pellucid Hawk Moth, <i>Cephonodes hylas</i> L (Lepidoptera: Sphingidae)

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  • オオスカシバ幼虫の体色と発育に及ぼす生息密度の影響
  • オオスカシバ ヨウチュウ ノ タイショク ト ハツイク ニ オヨボス セイソク ミツド ノ エイキョウ

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Abstract

The larger pellucid hawk moth is a common pest of cape jasmine, Gardenia jasminoides ELLIS in Japan. There are 4-5 generations in a year in Kyoto. The female moth lays eggs singly on the underside of leaves. It is well known that the larvae exhibit color variation in the field. The experiment was carried out in order to analyse the effect of population density during the larval period on the larval coloration and development. The larvae were reared at different densities of 1-5 individuals/plastic vessel, 12×3cm, at about 30°C. Most of the larvae kept in isolation since the hatching were pale green, but those reared in the densities of 2 or more individuals per vessel turned brown after the first moult and, from the beginning of the fourth instar, changed into dark brown or green with broad brown stripe dorsomesally. The highest degree of darkening appeared in the larvae kept under crowding conditions throughout the whole larval stage. The darkening was determined by the density of the first instar. The presence or absence of light not effective on the darkening. The isolated pale green larvae showed longer duration of life, larger food intake and higher rate of oxygen consumption than the crowded dark-colored ones. The mortality strongly increased and the weight of pupa significantly decreased with the rise of density, but neither duration of larval and pupal periods, head width nor body weight of larva (except the fifth instar) differed significantly according to the density. It might be concluded that the pale green larva found commonly in the field is a more adapted form as regards their natural mode of life than the dark-colored larva found at high density.

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