EFFECT OF LIGHT QUALITY AND LARVAL DIET ON MORPH INDUCTION IN THE POLYMORPHIC CATERPILLAR NEMORIA-ARIZONARIA (LEPIDOPTERA, GEOMETRIDAE)

The emerald moth Nemoria arizonaria (Geometridae) is bivoltine, with d istinct broods of caterpillars hatching in the spring and summer. Cate rpillars of the spring brood develop into mimics of oak catkins, while caterpillars of the summer brood develop into mimics of oak twigs. Pr evious rearing experiments showed that all caterpillars reared on oak catkins developed into catkin morphs, while all caterpillars reared on oak leaves developed into twig morphs, regardless of temperature or p hotoperiod. However, those previous rearing experiments did not contro l the colour of light perceived by the caterpillars independently of t heir diet. Since wavelengths of light perceived by some species of pol ymorphic caterpillars can influence their colour, it is possible that morph induction in Nemoria arizonaria is due to the characteristics of light reflected from yellow catkins or green leaves, rather than larv al diet itself. The experiments reported here independently varied lar val diet and light characteristics to determine if light quality is in volved in morph induction. Only larval diet influenced morph induction , since all caterpillars reared on catkins developed into the catkin m orph, and all caterpillars reared on oak leaves developed into the twi g morph, regardless of whether they perceived yellow light, preen ligh t, or were raised in the dark. (C) 1996 The Linnean Society or London