INFLUENCE OF WIND CONDITIONS AND INTERTRAP SPACING ON PHEROMONE TRAP CATCHES OF MALE EUROPEAN PINE SAWFLY, NEODIPRION-SERTIFER

The spatial distribution of catches of male European pine sawfly, Neod iprion sertifer (Geoffr.) (Hymenoptera, Diprionidae), was studied usin g different pheromone trap arrays. In hexagonal trap groups, trap inte rference was evident by reduced catch in the central of seven traps sp aced 10 to 40 m apart. When the trap spacings were either 5 or 80 m no significant reduction could be shown. The interaction was more pronou nced for strong (100 mu g) pheromone ([2S, 3S, 7S]-3,7-dimethyl-2-pent adecanyl acetate) lures than for weak ones (10 mu g). Similarly, the i nner traps caught less than the outer traps in grids of 6 x 6 traps sp aced 20 or 50 m apart. Mark-release-recapture experiments in the grid array confirmed that a majority of the males originated from outside t he trap group and were caught in the first trap they encountered. Ther e were no differences between catches in downwind, crosswind and upwin d traps. Thus, no 'overshooting' was evident during average conditions , i.e. the sawflies did not divert from the trap initially attracting them by flying to the upwind trap. However, the proportion caught in t he upwind traps increased with increasing wind velocity, suggesting mo re overlapping pheromone plumes at higher wind speeds. Also, the recap ture rate of released males increased with increasing wind velocity up to a daily average of 3.1 m/s at 2 m, indicating that sawflies more e asily find the pheromone source, probably due to a more stable pheromo ne puff trajectory during higher wind velocities. The application of p heromone traps in e.g. monitoring studies is discussed and a distance of at least 50 m between the traps with strong lures used in the prese nt study is recommended to avoid trap interaction.