INDIRECT MEASURES OF LARVAL DISPERSAL IN THE CINNABAR MOTH, TYRIA JACOBAEAE (LEPIDOPTERA: ARCTIIDAE)

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Abstract
Caterpillar dispersal among food plants is difficult to measure directly in field populations. However, the tendency of fifth instar cinnabar moth caterpillars to drop from plants when disturbed is correlated to measured larval dispersal in experimental populations. This easily executed behavioural test can therefore be used as an indirect indicator of dispersal in different populations. The degree of response of first and fifth instar cinnabar moth larvae to disturbance is correlated for eight populations tested, possibly indicating a common agent selecting for the falling reaction among larvae in these different stages of development. Many insects drop from their food plants in response to disturbance and we suggest that this behaviour might provide a useful tool to elucidate relationships between insect dispersal and resource exploitation.