Induction of host preference in Drosophila melanogaster.

Individuals of Drosophila melanogaster were maintained as larvae and/or as adults on media made from one of the following natural breeding sties: apple, tomato, banana, or squash. The oviposition site preference of adults was not affected by the type of food they had developed on as larvae. However, prior exposure to either apple or tomato enhanced their preference for that food when subsequently given a choice between apple and tomato for oviposition. In a second experiment, adult flies were kept on media made from either apples, oranges, grapes, tomatoes, or onions; their oviposition site preferences were subsequently tested in a 5-choice situation. Prior exposure to a particular food did in some cases increase the acceptability of that food to flies. More remarkably, it sometimes modified the flies' responses to other foods, a phenomenon referred to here as cross-induction.