Aggregation pheromones have a non-linear effect on oviposition behavior in Drosophila melanogaster

Female fruit flies (Drosophila melanogaster) oviposit at communal sites where the larvae may cooperate or compete for resources depending on group size. This offers a model system to determine how females assess quantitative social information. We show that the concentration of pheromones found on a substrate increases linearly with the number of adult flies that have visited that site. Females prefer oviposition sites with pheromone concentrations corresponding to an intermediate number of previous visitors, whereas sites with low or high concentrations are unattractive. This dose-dependent decision is based on a blend of 11-cis-Vaccenyl Acetate (cVA) indicating the number of previous visitors and heptanal (a novel pheromone deriving from the oxidation of 7-Tricosene), which acts as a dose-independent co-factor. This response is mediated by detection of cVA by odorant receptor neurons Or67d and Or65a, and at least five different odorant receptor neurons for heptanal. Our results identify a mechanism allowing individuals to transform a linear increase of pheromones into a non-linear behavioral response. Drosophila larvae may benefit each other at lower densities but compete at higher densities. Here, Verschut et al. identify a mechanism enabling Drosophila females to favor egg-laying sites containing medium concentrations of aggregation pheromones, which may facilitate choice of favorable sites.

Automated summary

Female fruit flies can assess the social information of their oviposition sites by detecting the concentration of pheromones left by previous visitors. They prefer sites with intermediate pheromone concentrations and avoid sites with low or high concentrations. This decision-making process is based on the detection of two different pheromones.