Oviposition preference for and positional avoidance of acetic acid provide a model for competing behavioral drives in Drosophila.

Selection of appropriate oviposition sites is essential for progeny survival and fitness in generalist insect species, such as Drosophila melanogaster, yet little is known about the mechanisms regulating how environmental conditions and innate adult preferences are evaluated and balanced to yield the final substrate choice for egg-deposition. Female D. melanogaster are attracted to food containing acetic acid (AA) as an oviposition substrate. However, our observations reveal that this egg-laying preference is a complex process, as it directly opposes an otherwise strong, default behavior of positional avoidance for the same food. We show that 2 distinct sensory modalities detect AA. Attraction to AA-containing food for the purpose of egg-laying relies on the gustatory system, while positional repulsion depends primarily on the olfactory system. Similarly, distinct central brain regions are involved in AA attraction and repulsion. Given this unique situation, in which a single environmental stimulus yields 2 opposing behavioral outputs, we propose that the interaction of egg-laying attraction and positional aversion for AA provides a powerful model for studying how organisms balance competing behavioral drives and integrate signals involved in choice-like processes.