‘Anemotactic’ flight paths of tsetse flies in relation to host odour: a preliminary video study in nature of the response to loss of odour

ABSTRACT. Free‐flying, wild Glossina pallidipes Aust. and G. morsitans Westw. were video‐recorded in the field in Zimbabwe as they flew out of air permeated with host odour (camera 2.5 m up, looking down at the ground). Analysis of the flight tracks supports the proposal of Bursell (1984) that tsetse flies attracted to an invisible source of host odour respond weakly if at all to wind direction while in flight: on losing contact with the odour the flies made a sharp turn that was uncorrelated with wind direction. The size of the turn varied considerably, with a marked discontinuity in the log‐survivorship curve at 120° (a fly which had turned through at least 120° was 5 times as likely to stop the turn as a fly which had turned <120°). Over half the flies made turns of >90° (and <2 m diameter) within the 2×2.5 m field of view of the camera. It is suggested that these turns initially served to arrest the upwind progress of the fly, with the size of the turn determining the degree to which the fly backtracked towards where it last detected odour or continues cross‐wind. Mean flight speed was c. 5 ms‐1 (min. 2.5, max. probably 7ms‐1).

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