Upwind flight responses of tsetse flies (Glossina spp.) (Diptera: Glossinidae) to acetone, octenol and phenols in nature: a video study

Video observations were made of tsetse flies (mainly Glossina pallidipes Austen) as they approached, responded to and left a vertical (I m square) black target in odour plumes of acetone, or a 4:1:8 mixture of octenol:propylphenol: methylphenol, or acetone plus this "4:1:8" mixture, or in no odour. No differences in mean flight speed or turn size in any of these situations were detected. With the odour source 5 m upwind of the target, the flight tracks of tsetse arriving at and leaving the target were significantly biased towards upwind, highly so when 4:1:8 was present, marginally so in acetone alone. With the source 10 m upwind, the same biases were still present but weaker. Circling flights around the black target were more frequent in acetone plus 4:1:8 than in no odour (26% vs 15%), but in either odour alone were only just significantly more than in no odour. Upwind turning at the target was more frequent (25% vs 17%) in acetone alone that in no odour (though not in 4:1:8 alone). It is concluded that 4:1:8 elicits an upwind anemotactic response comparable in strength to that in CO2, and that acetone elicits a similar response more weakly, but may be more involved in potentiating visual responses. Introd uction know whether they do in fact have this effect in the field, but that it has simply not been detected. We examined this question by recording the flight tracks of tsetse with video in Zimbabwe, using acetone and the combination of octenol and phenols now used commonly to bait targets and traps in fly control programmes. We report here on the analysis of these tracks.