Range expansion of Hyposidra talaca (Geometridae: Lepidoptera), a major pest, to Northeastern Indian tea plantations: change of weather and anti-predatory behaviour of the pest as possible causes

Abstract

Hyposidra talaca (Walk.) is a major pest of tea (Camellia sinensis L.) in Northeastern (NE) India. The present study examined (1) the likely causes of expansion of H. talaca to tea from its ancestral home of sal forests, and (2) the anti-predatory mechanisms that helped it to build up in tea plantations. Studies were made on the role of the regulating agents of the eggs and caterpillars of the pest and responses of caterpillars to different predator-like stimuli (predatory wasps, ants and birds) and mechanical vibrations. Eggs collected from the fields were reared in the laboratory to study egg parasitization and monitored in the field to study the role of natural predators. Prolonged drought and inconsistent rainfall influenced the range expansion of H. talaca. In tea plantations, female moths preferred to conceal the eggs in the scaly bark of shade trees. Excluding woodpeckers, H. talaca eggs were scarcely attacked by other natural enemies. The caterpillars dropped off the plant in response to potential predators and assumed a deimatic ‘U’ or ‘S’ shape, and remained motionless when stimulated by mechanical vibration. This study suggests that the lack of specialized natural enemies helped H. talaca to build up in the tea plantations of NE India in a short period of time.