Upwind anemotaxis in response to cue-lure by the Queensland fruit fly, Bactrocera tryoni

Movements of mature male Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) were observed individually in a wind tunnel under conditions of ‘cue-lure with wind’, ‘cue-lure with no wind’, ‘wind only’ and ‘no wind or cue-lure’. Further observations were made using a dense foliage array in the wind tunnel and a structured plume of cue-lure. Patterns of walking or flying were essentially the same in all of the first four treatments except that in the ‘cue-lure with wind’ treatment, over half of the flies moved in a consistent track upwind for at least 400 mm at some time during the first 5 min of observation. With clean wind, only 10% of the flies did this. The result was that mean net upwind displacement after 5 min in the ‘cue-lure with wind’ treatment significantly exceeded that in the other three treatments, the results of which did not differ significantly from each other. The upwind tracks were accomplished by either walking or flying (with or without stops) or by a combination of both. When the wind tunnel was filled with a dense foliage array, the results with cue-lure laden wind were similar to those obtained with the equivalent treatment without foliage, except that upwind tracks were predominantly in short stages. When flies were exposed to a structured plume of cue-lure odour (without foliage present), they did not apparently alter their behaviour on leaving or entering the plume, but some did make consistent upwind tracks while they were in the plume.