1CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia. 2Universität Bayreuth, Lehrstuhl Tierphysiologie, 95440 Bayreuth, Germany.
The labial gland of the French termite Reticulitermes santonensis contains a water soluble, heat-resistent chemical signal. It is released directly onto the food during gnawing and feeding and stimulates feeding in nestmates. Thin layer chromatography of the labial gland secretion on cellulose plates combined with a subsequent feeding bioassay revealed that 95% of the termites were feeding between Rf 0.46 and 0.88. Thirty-five synthetic chemicals of similar chemical properties as the feeding stimulating signal were analyzed with TLC and feeding choice tests on filter paper. None of them covered the biologically active zone, and termites showed feeding preference only to sugar-like components and some amino acids at unphysiologically high concentrations. A feeding choice test on filter paper showed that labial gland secretions of 11 further termite species all stimulated feeding both in R. santonensis and in the African termite Schedorhinotermes lamanianus, a species which had been shown to as well carry the feeding stimulating signal in its labial gland secretion. The combined TLC-feeding bioassay on cellulose plates showed that the signal is located between Rf 0.46 and 0.88 in all 11 species. The heat resistance of the signal could also be shown in selected species. An extract of the labial glands of cockroaches stimulated feeding in R. santonensis and S. lamanianus as well, but was no longer effective after heat treatment and after TLC. This points towards a general feeding stimulating signal present in the labial gland secretion of all Isoptera.