UPWIND FLIGHT OF TSETSE (GLOSSINA SPP) IN RESPONSE TO NATURAL AND SYNTHETIC HOST ODOR IN THE FIELD

In Zimbabwe, studies were made of the flight responses of tsetse (Glos sina spp.) to synthetic and natural ox odour using arrangements of ele ctric nets. Tsetse flying away from a target showed a significant upwi nd bias when a blend of carbon dioxide (2 1/min), acetone (500 mg/h), octenol (0.4 mg/h), LE-methylphenol (0.8 mg/h) and 3-n-propylphenol (0 .1 mg/h) was dispensed 15 m upwind, with c. 35% flying upwind. Without carbon dioxide this percentage was significantly reduced to 15% which was not significantly different from that with no odour (8%). This pa ttern was not altered by reducing the doses of acetone, octenol and ph enols by 10-100 times, to levels comparable to those produced by an ox . With natural ox odour or a synthetic equivalent of ox odour dispense d from a ventilated pit 8 m upwind of the target, c. 28% flew upwind. This was reduced significantly to 15% if carbon dioxide was removed. I n studies using a 17 m line of nets arranged orthogonally across the p revailing wind line, c. 50% of the catch was caught on the downwind si de in the absence of odour. This increased significantly to c. 60% whe n acetone, octenol and phenols were dispensed 15 m upwind, with or wit hout carbon dioxide. With a shorter line (9 m) or an incomplete one (1 6.5 m long with 5 x 1.5 m wide gaps along its length) there was no cha nge in the proportion caught downwind. For all three lines, dispensing odour upwind increased the catch 2-5 times on both the up- and downwi nd sides of the nets. It is concluded that a stronger upwind response to host odour is elicited when carbon dioxide is present. It is sugges ted that in nature upwind flight is very imprecisely orientated, with tsetse making flights up and down an odour plume 'searching' for a hos t.