ON THE RESPIRATORY QUOTIENT (RQ) OF TERMITES (INSECTA, ISOPTERA)

The respiratory quotient (RQ) at 28 degrees C was determined by Warbur g manometry in 23 species of termites from the Mbalmayo Forest Reserve (Cameroon) and three sub-tropical species cultured under laboratory c onditions in the U.K. or freshly collected in Australia. The data are tabulated with other recently reported RQs (determined by manometry or GC) and with measured CH, emission rates to provide a survey of 29 sp ecies covering both lower and higher termites in all major trophic (fu nctional) categories, In all species, except the wood-feeding Coptoter mes acinaciformis and the soil-feeding Cubitermes fungifaber, the obse rved mean values (with manometry corrected for known fluxes of H-2 and CH4) were at or well above 1.00, Soil-feeding forms (except C. fungif aber) generally showed a high apparent RQ (not corrected for H-2), wit h nine species (out of 13) above 1.20 and six species above 1.30, Well -replicated laboratory experiments with Reticulitermes lucifugus showe d that there was a tendency for RQ to fall with time over a 4-h incuba tion, although remaining greater than 1.00. The observed RQs are consi stent with carbohydrate being the principal substrate supporting respi ration in. all trophic and. taxonomic categories, with little or no co ntribution from the degradation of lignin or other polyaromatic materi als, However, in many species (especially soil-feeders), the observed RQ is greater than that expected from known fluxes of O-2, CO2 and CH4 on the assumption that carbohydrate is the respiratory substrate, Thi s presupposes that there is a large hydrogen sink (additional to CH, p roduction), possibly the emission of H-2 gas, and/or the existence of unresolved digestive mechanisms or electron routings, Uncertainties in the use of manometry with termites are discussed. (C) 1997 Elsevier S cience Ltd.