In search of a model system for exploring the Chemical Legacy Hypothesis:Drosophila melanogaster and geraniol.

We required an experimental system in which to explore elements of the chemical legacy hypothesis, according to which molecules of environmental chemicals may persist on or in the body or immediate surroundings of larval or pupal insects and influence their habitat preferences in adulthood by affecting the maturation of the chemosensory pathways. Using a purpose-built apparatus which exploited the geotactic and phototactic behavior ofDrosophila melanogaster, we examined the pattern of responses to a range of dilutions of geraniol, a terpene of plant origin. Fruit flies avoided the geraniol at high concentrations. Although attraction at low doses and reduced aversion after larval, pupal, or early adult exposure to geraniol have been reported, we did not find either. Thus, we failed to generate the phenomenon described as "pre-imaginal conditioning" required for the model system. We discuss the results in relation to designing suitable assays for testing the Chemical Legacy Hypothesis.