The responses of individual males in an isolated population of Glossina morsitans morsitans Westwood (Diptera: Glossinidae) to pheromone-baited decoy ‘females’

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Abstract
The responses of individually marked males of Glossina morsitans morsitans Westwood to decoys (9 × 3-mm rectangles of 2-mm-thick brushed nylon) baited with sex pheromone (15,19,23-trimethylheptatriacontane) were studied after their release onto an island in Lake Kariba, Zimbabwe. Some 45–60% of resighted flies were seen on decoys, the percentage being greater for flies released at an older age. For flies released on emergence, the mean age at first contact with decoys on a static screen was 6.6 days, an average of four days later than their first observed contact with a bait ox. There was great variability in the response towards decoys on successive contacts. In general, the intensity of the responses to decoys in the first minute after contact (the ‘pre-copulatory’ responses) decreased from one enounter to the next in a single 1–2-h observation session, but were restored to high levels after an interval of several hours. The intensity of responses towards decoys after this initial period (the ‘copulatory’ responses) were not affected by previous contacts. Neither previous sexual experience nor age at first contact affected the durations of response on decoys. There were no differences between the responses of wild flies and those from a laboratory colony. The results are discussed in relation to the use of decoys with chemosterilant for tsetse autosterilization. Over 60% of flies contacting decoys did so more than once, which would increase, cumulatively, the chances of their being sterilized.

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