EFFECT OF DIET EXPERIENCE ON THE ABILITY OF DIFFERENT LARVAL CHEMOSENSORY ORGANS TO MEDIATE FOOD DISCRIMINATION BY THE TOBACCO HORNWORM, MANDUCA-SEXTA

The effects of different diets on the role of each of five chemosensory organs in food discrimination was examined by measuring food preferences of larvae of the tobacco hornworm, Manduca sexta, which have different chemosensory organs remaining after microsurgery. Food preferences of fifth-instar larvae, reared on Lycopersicon esculentum or Vigna sinensis, were determined in two-choice tests using discs of V. sinensis and wetted filter paper discs (control). Larvae reared on L. esculentum are deterred from eating V. sinensis when either the epipharyngeal sensilla or the medial or the lateral maxillary sensilla styloconica are remaining. Only the latter organs confer the normal level of rejection of this plant. In contrast, the maxillary palps provide input which results in a preference for this plant and the antennae do not mediate any detectable discrimination. Thus, responses to V. sinensis vary depending on the chemosensory organ used. Larvae reared on V. sinensis prefer this plant over control. The individual chemosensory organs of these larvae mediate food discrimination which are similar to those of larvae reared on L. esculentum, except for the antennae. Larvae with antennae remaining prefer V. sinensis over control to the same degree as normal larvae do. Thus, rearing larvae on V. sinensis instead of L. esculentum enhances the acceptability of this plant which may involve a change in the weighting factor of antennal input.