Mass trapping of the spruce bark beetle Ips typographus L.: traps or trap trees?

Abstract

Standing live trap trees are one of the most commonly used trapping techniques against Ips typographus in Belgium. In this paper we present experiments designed to compare their efficiency for mass trapping against commercial Theysohn slot traps, in terms of numbers of insects killed. To begin with, a method to estimate the total number of beetles killed by a standing trap tree is developed. Traps and trap trees were presented to the beetles both separately (in experiments where the position of the traps and trap trees were changed each time the site was visited) and together (in such a way that the beetles were facing a binary choice). 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, as they usually are, 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.