RATE OF REALIZED INTERCEPTION OF PHEROMONE PULSES IN DIFFERENT WIND SPEEDS MODULATES ALMOND MOTH ORIENTATION

The interception of a pheromone filament induces flying moths to surge briefly nearly straight upwind; in the absence of pheromone moths cea se upwind progress and zigzag crosswind. We tested males of the almond moth, Cadra cautella (Lepidoptera, Pyralidae), in a low-turbulence wi nd tunnel in wind velocities of 20, 40 and 80 cm s(-1). A mechanical p ulse generator was set to produce plumes either with same pheromone pu lse frequency (pulse generation frequency of 2.9 Hz, interpulse distan ces from 7 cm to 28 cm) or plumes with same interpulse distance across the three wind velocities (interpulse distance of 14 +/- 2 cm, pulse generation frequency of 1.7-5.0 Hz). In plumes of similar pulse freque ncy, the faster the speed of the wind the slower the ground speed of f light. However, in plumes of similar interpulse distance, ground speed remained relatively constant independent of the wind speed. A 'realiz ed' frequency of pulse interception for males flying along the various combinations of pulse frequencies and wind velocities was calculated using the males' average airspeed and the spatial distribution of pher omone pulses in the plume. Realized frequency of pulse interception ra nged from 1.3- to 3.0-fold higher than the frequency of pulse generati on. The flight tracks of males reflected the regime of realized pulse interception. These results suggest that upwind flight orientation of male C. cautella to pheromone in different wind velocities is determin ed by the flux of filament encounter.