In insects, increasing evidence suggests that small secreted pheromone binding proteins (PBPs) and odorant binding proteins (OBPs) are important for normal
olfactory detection of airborne pheromones and odorants far from their source
1,
2,
3,
4,
5,
6 and
7. In contrast, it is unknown whether extracellular ligand binding proteins participate in perception of less volatile chemicals, including many pheromones, that are detected by direct contact with chemosensory organs. CheB42a, a small
Drosophila melanogaster protein unrelated to known PBPs or OBPs, is expressed and likely secreted in only a small subset of gustatory sensilla on males' front legs, the site of gustatory perception of contact pheromones
[8]. Here we show that
CheB42a is expressed specifically in the
sheath cells surrounding the taste neurons expressing
Gr68a [9], a putative gustatory pheromone receptor for female cuticular hydrocarbons that stimulate male courtship
[10]. Surprisingly, however,
CheB42a mutant males attempt to copulate with females earlier and more frequently than control males. Furthermore,
CheB42a mutant males also attempt to copulate more frequently with other males that secrete female-specific cuticular hydrocarbon pheromones, but not with females lacking cuticular hydrocarbons. Together, these data indicate that
CheB42a is required for a normal gustatory response to female cuticular hydrocarbon pheromones that modulate male courtship.