New isoforms of odorant-binding proteins and potential semiochemicals of locusts.

To obtain more information on the elements of chemical communication in the migratory locust (Locusta migratoria) (Orthoptera: Acrididae), we have searched for additional odorant-binding proteins (OBPs) and for volatiles in the feces that could represent potential semiochemicals for this species. A two-dimensional electrophoretic (2DE) analysis of an antennal extract showed only three closely positioned spots that were recognized by the antiserum against locust OBP. Three genes were also identified using PCR and 5'RACE-PCR approaches, encoding isoforms differing from each other for a single amino acid substitution. The gas-chromatographic-electroantennogram (GC-EAD) headspace analysis of a feces sample revealed the presence of several compounds that elicited dose-dependent electrophysiological responses in the antennae of both sexes. Most of these compounds are different from those identified in the feces of the desert locust (Schistocerca gregaria) and reported to be behaviorally active. Ligand-binding experiments performed with such volatiles and recombinant OBP did not show affinity, thus indicating that the binding pocket of OBP requires larger molecules than those so far identified.