Mass trapping of the spruce bark beetle Ips typographus L.: traps or trap trees?
Standing live trap trees are one of the most commonly used trapping techniques against Ips typographus in Belgium. Tests were undertaken in three different spruce [Picea abies] stands in southern Belgium to compare the efficiency of Theysohn slot traps and standing live trap trees, tested both together and separately, in terms of numbers of insects killed. When presented separately, trap trees caught at least 1.7-3.5 times as many bark beetles as traps. However, towards the end of the experiments, their superiority decreased because of the more exposed position of their dispensers that emptied faster. In the binary-choice experiments, this decrease could be avoided by protecting the dispensers from sun and wind with a portion of PVC piping and by exposing the traps' dispensers. When the dispensers were exposed on the trap trees and protected inside the traps, trap trees caught 3.4-4.0 times as many beetles as the traps; when the traps' dispensers were exposed and the trap trees' dispensers protected, this ratio increased to between 8.5 and 31.4. In practice, however, it was not clear whether this protection would produce a major reduction in the catches during the beginning of a trapping campaign, or if the additional catches performed during the end of this campaign could compensate for the reduction. Nevertheless, protected dispensers have a more constant attractive power and might provide a more secure control of bark beetle populations.