Making shelter for enemies: parasitoid-induced shelter-building behaviour in Paraponyx stagnalis

Abstract

ABSTRACT Manipulative parasitoids manipulate the behaviour of their hosts in such a way as to benefit their own offspring. Paraponyx stagnalis Zeller is a leaf case worm caterpillar pest of rice and pupates in cases made out of cut leaf blades. These shelters are typically open-ended tubular cases. Its solitary primary endoparasitoid – Apanteles sp. – triggers changes in the way it sews the cases. The observed changes in the folded leaf shelter may serve various functions for the developing parasitoid, such as minimising the risk of hyperparasitism and predation, and enhancing structural stability. To obtain evidence to support these hypotheses, we (1) documented the morphotype of the cases/puparia constructed by unparasitised and parasitised P. stagnalis larval instars, (2) studied the overall rate of primary parasitism of P. stagnalis by Apanteles sp. and (3) studied the rate of hyperparasitism of primary parasitoids in 10 rice fields of south India. Unlike the unparasitised third-instar host larvae, the parasitised larvae sealed the open ends of the folded leaf shelter with silken threads, affixed the puparium to rice leaves and made small cases. The overall parasitism rate was about 40%. However, the hyperparasitism was between 0.6 and 1%. Though the primary parasitism by Apanteles sp. is considerably higher in all 10 fields, the meagre incidence of hyperparasitism strengthens our hypothesis that the modified puparium construction might be triggered by the primary parasitoid and beneficial for the offspring of the primary parasitoid. Our field observations suggest that future experimental studies can bring mechanical evidence for host manipulation by Apanteles sp.