Modulation of whitefly take-off and flight orientation by wind speed and visual cues

The effect of different wind speeds on take-off and flight orientation of t he sweetpotato whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), was studied in the presence of a green visual stimulus which reflected 550 +/- 10 nm light, or a white stimulus of the same intensity. When the white light was present, take-off was negatively correlated with wind speed. Ana lysis of the flight tracks of whiteflies in 0, 15 and 30 cm/s wind with the white light present showed that flight was not directed toward the stimulu s in zero wind, and that insects were carried downwind as the wind increase d. Net displacement downwind was significantly slower than the wind speed, indicating that B. tabaci can control its rate of displacement relative to its surroundings, and is not always passively transported by the wind. In t he presence of the green visual stimulus, take-off and flight behaviour of B. tabaci was markedly different to that observed in the presence of the wh ite light. Taking off was more likely and whiteflies made upwind orientated flights, landing on the illuminated section of the screen when it reflecte d green light. At all wind speeds tested, the mean ground speeds of B. taba ci were approximately 20 cm/s whether the insects were flying upwind or dow nwind. This uniformity of ground speed regardless of the changing effects o f wind-induced drift in different directions strongly suggests that whitefl ies actively control their ground speed using visual flow fields in a manne r similar to all other flying insects examined thus far.