INFLUENCE OF PLUME STRUCTURE AND PHEROMONE CONCENTRATION ON UPWIND FLIGHT OF CADRA-CAUTELLA MALES

The effects of pheromone plume structure and its concentration on the pheromone-mediated flight of male Cadra cautella (Lepidoptera: Phyciti nae) were investigated in a laminar-flow wind tunnel. When two C. caut ella males flew simultaneously along a ribbon plume of mixed smoke and pheromone, their in-flight behaviour was dependent on the instantaneo us structure of the plume they encountered. When a male intercepted an intact ribbon filament, he sustained a crosswind course, whereas when he intercepted a turbulent filament (created by an upwind male fragme nting the ribbon plume), he adopted a flight course more due upwind. T hese results indicate that C. cautella males altered their in-flight m anoeuvres in response to instantaneous changes in the fine structure o f the pheromone plume. We also demonstrated that differences in the fi ne structure of the plume had more influence on the flight pattern of C. cautella males than a 1000-fold range in pheromone dose. The size o f the plume was increased by adding wind deflectors upwind of the pher omone source. Independent of source dosage, males following ribbon plu mes flew slow zigzag tracks, whereas males following large, turbulent plumes flew directly to the source in fast, straight tracks with less counterturning.