Dose-dependent response and preliminary observations on attraction range of Ips typographus to pheromones at low release rates

Responses of the European spruce bark beetle, I. typographus (Coleoptera: Scolytidae), to low release-rate pheromones were investigated in two experiments in a spruce forest at Wellin, southern Belgium. Dose-response of the beetle was first examined in a trapping experiment in August 1999. The major pheromone components of I. typographus, (S)-cis-verbenol (cV) and 2-methyl-3-buten-2-ol (MB) were released from window traps. Five treatments were replicated five times: (1) blank trap, (2) 0.03 and 1.2, (3) 0.11 and 4.5, (4) 0.34 and 15.2 mg/day of cV and MB, respectively, and (5) Pheroprax. Trap catches increased linearly as a function of increasing release rates of cV and MB. A second study aimed at making preliminary observations on the attraction range of the pheromones as compared to Pheroprax. A release-recapture experiment was carried out in May 2000: four trap-trees located 50 m away from a central release platform were equipped with window traps baited with increasing release rates, tested in separate releases: 0.03 and 1.2; 0.11 and 4.5; 0.34 and 15.2 mg/day of cV and MB, respectively, and Pheroprax. Recaptures increased with the release rate. Trap catches were different at lower release rates, but not between the release rate of 15.2 mg/day of MB and Pheroprax. Variations in captures in relation to wind parameters showed persistently random flight at the lower release rates. Significant upwind flight was observed for Pheroprax only. These results imply that trap interference existed for Pheroprax and suggest that its attraction range may be greater than 50 m.