Preimaginal conditioning in Drosophila revisited

During metamorphosis, the nervous system of a holometabolous insect changes significantly. Attempts to demonstrate preimaginal conditioning, here take n to mean the retention of learning through metamorphosis, have given mixed results. We used two behavioural assays (the T maze and trap assay) to see whether a change in adult responsiveness could be induced by exposing Dros ophila melanogaster larvae to a conditioning stimulus. There was no evidenc e for preimaginal conditioning from either assay, but the trap assay demons trated that menthol contamination from the larval environment on the pupari al surface could induce a change in adult behaviour. Exposure of adult inse cts to this contamination could give the appearance of preimaginal conditio ning, when in fact the behavioural induction occurred during the adult stag e. Young flies responded less strongly than older flies to the odour cues i n both assays. This may explain the apparently contradictory findings of so me earlier studies of preimaginal conditioning. (C) 1999 The Association fo r the Study of Animal Behaviour.