ELECTROANTENNOGRAM RESPONSES OF TSETSE-FLIES (GLOSSINA-PALLIDIPES) TOHOST ODORS IN AN OPEN-FIELD AND RIVERINE WOODLAND

The present study was initiated to gain insight into the way in which tsetse flies (Glossina spp.) sense odours at different locations in od our plumes in both an open field and a wooded area. We recorded the an tennal responses (EAGs) from stationary living female G. pallidipes 15 m upwind and at various (60, 40, 20, 10, 5 and 1 m) distances downwin d from a synthetic host odour source (containing 1-octen-3-ol, acetone and two phenols), in the natural habitat of the fly (Zimbabwe) using a portable electrophysiological device. Experiments were performed in a flat open area (an airstrip) and in riverine woodland. Differences b etween responses in different environments were determined by comparin g various parameters of the EAGs (intermittency, frequency, amplitude, duration and rate of depolarization). We found that a fly senses odou rs as puffs that, further downwind, contain less odour and pass less f requently. In an open field downwind from the source, tsetse perceive more olfactory information than upwind for only 10-20 m, whereas in wo odland, olfactory responses remain higher and more frequent than upwin d up to at least 60 m. In an open field, olfactory information rapidly increases when approaching the odour source from 20 m and in woodland from 5 m onwards. It is proposed that averaging odour information ove r time may be of minor importance in long-range location of odour sour ces. The results suggest that tsetse may smell odour-baited targets fr om at least 60 m downwind and that the number of flies responding to a nd being caught by these baits may be higher in woodland than in an op en field.