Are odorant-binding proteins involved in odorant discrimination?

Pheromone-sensitive sensilla trichodea of nine moth species belonging to six families and three superfamilies of Lepidoptera were immunolabelled with an antiserum against the pheromone-binding protein of Antheraea polyphemus. Strong immunolabelling of the sensillum lymph was observed in all long sensilla trichodea of A. polyphemus, A. pernyi (Saturniidae), Bombyx mori (Bombycidae) and Manduca sexta (Sphingidae). Very weak labelling was found with all sensilla trichodea of Dendrolimus kikuchii (Lasiocampidae) and Lymantria dispar (Lymantriidae). In three noctuid species, some long sensilla trichodea were labelled strongly, some only weakly and some were not labelled at all. The fraction of long sensilla trichodea that were strongly labelled was large in Helicoverpa armigera, but small in Spodoptera littoralis and Autographa gamma. The observed cross-reactivity was not correlated with taxonomic relatedness of the species but rather with chemical relatedness of the pheromones used by these species, as a high labelling density was consistently observed in sensilla tuned to pheromones with an alcyl chain of 16 carbon atoms. The highly divergent specificity of pheromone-receptor cells in Noctuidae appears to be mirrored by a similar diversity of the pheromone-binding proteins in the sensilla trichodea. These data support the notion that pheromone-binding proteins participate in odorant discrimination.