Food exploitation in termites: Indication for a general feeding-stimulating signal in labial gland secretion of isoptera

The paired labial glands are located in all termite species in the thorax. During food exploitation workers of the French termite Reticulitermes santo nensis and the African termite Schedorhinotermes lamanianus release the sec retion of their labial glands directly onto the food. The secretion carries a water-soluble, heat-resistant, nonvolatile signal that stimulates gnawin g and feeding and leads to aggregations of feeding workers. In a Feeding bi oassay, extracts of the labial glands of II termite species from five famil ies all proved to have this feeding-stimulating effect both on R. santonens is and S. lamanianus. The heat resistance of the feeding-stimulating signal also could be shown for selected species from all termite families tested. A combined thin layer chromatography-feeding bioassay on cellulose TLC pla tes showed that after chromatography of labial gland secretion, the feeding -stimulating signal is located in all 11 species in the same area from R-f 0.46 to 0.88. An extract of labial glands of cockroaches stimulated feeding in R. santonensis and S. lamanianus as well, but was not active after heat treatment and after TLC. This points towards a general feeding-stimulating signal having evolved only in the labial gland secretion of termites.