Field Testing of a Putative Larviposition Pheromone for the Tsetse Fly Glossina m. morsitans Westwood

Under laboratory conditions, the alkane hydrocarbon n-pentadecane attracts gravid female tsetse (Glossina morsitans morsitans Westwood) to potential larviposition sites. We describe field-testing of this chemical, which is the first such test for any putative tsetse larviposition pheromone. We replicated randomised block experiments at 11 sites near Rekomitjie Research Station, Zambezi Valley, Zimbabwe. Each site comprised a cluster of four artificial warthog burrows constructed from 200-litre steel drums. We placed six trays, filled with sand and covered with leaf litter, inside each burrow. Both species of tsetse inhabiting this region entered these artificial burrows and deposited 1282 pupae in the trays during the experiments. In 13 experiments, n-pentadecane was tested at three different concentrations against a control. We were unable to find any conclusive evidence that the presence of n-pentadecane resulted in an increased larviposition rate for either G. m. morsitans or G. pallidipes. This finding was independent of the concentration of n-pentadecane used, and was not influenced by the presence or absence of added water, acetone or warthog urine. Any small effect of the pheromone is likely masked by the important physical characteristics of burrow larviposition sites. Order of magnitude increases in larviposition rates when leaf litter was added to larviposition sites were far greater than those due to the use of putative larviposition pheromones.