Loss of phototaxis in silkworm larvae after smelling mulberry leaves and recovery after electroconvulsive shock

Abstract

NEWLY hatched larvae of the silkworm Bombyx mori show a strong phototactic response to ultraviolet (357 nm), green (557 nm) and yellow (585 nm) light, but this is lost rapidly after they are fed on fresh mulberry leaves¹, as reported for some lepidopterous caterpillars^2,3. After being fed on an artificial diet containing neither mulberry leaves nor their extract, silkworm larvae continue to be phototactic (our unpublished data). Thus loss of the phototactic response is not caused by the stimulus of feeding, for example through a signal from the pharynx or abdomen. A chemical stimulus from mulberry leaves seems to affect the response directly. Chemicals of plant origin, which are perceived through the sense organs, have been found to elicit or repress some insect behavioural responses⁴, but little is known of the effect of the odour of food plants on the phototactic response of insects. We report here that silkworm larvae temporarily lose their normal phototactic response after smelling mulberry leaves and that a moderate electroconvulsive shock restores the response.