Quantifying relative importance of maxillary palp information on the olfactory behavior of Drosophila melanogaster.

Maxillary palps have been proposed as secondary olfactory organs, after the antennae, in Drosophila melanogaster. Our study tries to establish the quantitative importance of both organs as olfactory information mediators. Dose-response curves for three odorants: ethyl acetate, propionaldehyde and benzaldehyde were carried out for comparing olfaction in either complete animals or flies surgically deprived of antennae. Antennaless flies tested in our behavioral assay showed indifferent, attractant and repellent responses depending on concentration, similarly as normal flies do. However, they clearly displayed less sensitivity than normal flies. The range of concentrations they were able to perceive was correlated to antennal sensitivity approximately by a factor 1:10 for ethyl acetate and benzaldehyde, and between 1:10 and 1:100 at high concentrations of propionaldehyde. A complementary experiment was performed to test changes in olfactory behavior produced by removing maxillary palps in the presence of antennae. At high concentrations of odorant, responses to ethyl acetate and propionaldehyde experienced small changes when both palps were removed. Results are compatible with a summation model of all olfactory information reaching the brain either through antennae or palps.