Ontogenetic changes in the shelter site of a leaf-folding caterpillar, Vanessa indica

摘要

Factors responsible for ontogenetic habitat shifts were examined using larvae of the Indian red admiral butterfly, Vanessa indica (Herbst) (Lepidoptera: Nymphalidae). The larvae of V. indica fold leaves of China ramie, Boehmeria nipononivea Koidz. (Urticaceae), to form shelters that also serve as food. When constructing shelters, old larvae (usually third instar or older) frequently cut trenches at the bases of the leaves, whereas younger larvae do not. This trenching behaviour reduces the force required to fold large ramie leaves. Young larvae used small apical leaves as shelter sites. Once larvae were capable of cutting trenches, they moved proximally on the host plant and used middle leaves that either had completed or were about to complete expansion. Results of bioassays revealed that, for young larvae, apical and middle leaves did not differ in food quality. In contrast, for older larvae, the quality of middle leaves was higher than that of apical leaves. These observations suggest that young larvae decrease the risk of predation during shelter construction by using apical leaves that are relatively easy to fold, and that old larvae employ trenching to decrease the duration of leaf folding and improve growth rate by using middle leaves that are of high quality. Thus, the facilitation of leaf-folding by trenching is considered to reduce the necessity of using apical leaves, and the acquisition of the trenching ability triggers an ontogenetic shift in the selection of larval shelter sites.