The effect of leaf geometry on the feeding behaviour of the caterpillar of Manduca sexta (sphingidae)

Abstract

The fifth instar larvae of Manduca sexta, while remaining near the petiole, usually bent large ovoid leaves and then ate them fully. Long narrow leaves were not chewed off, but after some initial feeding near the base, were also bent and eaten from the tip to the petiole. The pattern in which variously shaped leaves were eaten was consistent for a given leaf shape and size. However, it could be altered by changing the flexibility and taper of the midrib. Sight appeared to be unimportant for feeding, but ablation of the antennae and maxillae (which normally moved in unison with the mandibles) caused the caterpillars to take less uniformly sized bites from the leaf and to have a slower rate of weight gain. Apparently the seemingly purposive behaviour of leaf bending which results in the economical harvesting of naturally hanging leaves arises from: (1) physical parameters of the leaf which restrict the larvae, (2) preferences of the larvae for immediately available leaf-edge, (3) coordination of the mouth-parts in relation to the leaf-edge, and (4) feeding forward in consecutive strips and sections. The behaviour therefore appeared to be non-specific and equally adapted to all leaf shapes.