EFFECT OF THE FINE-SCALE STRUCTURE OF PHEROMONE PLUMES - PULSE FREQUENCY MODULATES ACTIVATION AND UPWIND FLIGHT OF ALMOND MOTH MALES

The effects of plume intermittency and volume on behavioural and flight responses to pheromone of male Cadra cautella (Walker) (Lepidoptera: Phycitinae) were investigated in a pulling wind tunnel. The fine-scale structure of turbulent pheromone plumes was mimicked and manipulated using a pulser device that generated continuous ribbon plumes or intermittent plumes with defined pulse frequency and volume. As pulse frequency increased from 0.6 to 5 Hz and injected volume increased from 0.5 to 5 ml s(-1), males flew progressively higher air and ground speeds, turned less frequently, and steered smaller course angles, resulting in straighter flight tracks. The faster the frequency of pulses and the greater the volume of the plume, the higher the proportion of males responding, the shorter their latencies, and the less time spent in the behaviour. Flight tracks of male C.cautella to point sources of pheromone depend on the frequency of filaments encountered.