Impact of the western balsam bark beetle, <i>Dryocoetes confusus</i> Swaine (Coleoptera: Scolytidae), at the Sicamous Creek research site, and the potential for semiochemical based management in alternative silviculture systems

Abstract

Two pre-harvest baiting regimes were tested for their effect on Dryocoetes confusus in select stands at the Sicamous Creek Silviculture Systems Project. Single tree and two tree bait treatments, in addition to a control area, were established in a grid format throughout the research area. There were significantly more new D. confusus attacks in the baited areas than in the control area. Eighty percent of mass attacks occurred within 9 m of single tree bait centres, while 75% of mass attacks occurred within 10 m of twotree bait centres. Baiting appears to concentrate attacks into a discrete area and therefore could be used in single tree selection or patch cut systems (cuts generally less than 5 ha in size), two of the silviculture systems applied at the Sicamous Creek research area. Of 136 dead subalpine fir trees felled and examined, 105 (77%) showed clear evidence of D. confusus attack, making it the major cause of sub-alpine fir mortality at the Sicamous Creek research site. Naturally attacked trees had more advanced brood development and beetles utilized a greater percent of the total tree bole but had lower attack density (number of D. confusus galleries per unit area) than was observed on baited trees. In baited trees, the higher attack density resulted in indistinct gallery systems due to space competition of the brood. This suggested that there was a limited acceptable area for attack in these trees, which would not normally be susceptible. This study concludes it is possible to reduce resident populations of D. confusus by varying the number and placement of bait trees as a pre-harvest treatment.