Temperature requirements for western balsam bark beetle (Dryocoetes confusus Swaine (Coleoptera: Curculionidae: Scolytinae) development in southern British Columbia

The western balsam bark beetle, Dryocoetes confusus, is the primary biotic disturbance that is causing accelerated subalpine fir mortality in northern and high elevation forests in southern British Columbia.  B.C.’s climate has warmed dramatically over recent decades and is affecting many biological processes including those of D. confusus and its host subalpine fir.  D. confusus generally undergoes a two-year life cycle, with larvae and teneral adults each overwintering once.  To determine if it could have a univoltine life cycle, we reared D. confusus from field and laboratory-infested logs at five constant temperature regimes between 18°C and 24°C, with and without cold treatments.  In the coolest 18°C regime, development was arrested in the late larval stage indicating that an environmental cue was needed for development to proceed or not.  At temperatures higher than 21°C D. confusus displayed continuous development to teneral adult and emergence without requiring a cold period.  Our results demonstrate that D. confusus does not have an obligatory diapause, requiring 1,200 degree-days to complete development and that under warming field conditions it may be able to switch to a univoltine life cycle.  A life cycle contraction could have enormous implications to the future health of subalpine fir forests

Life history and pheromone response in Pissodes schwarzi Hopk. (Coleoptera: Curculionidae)

Pitfall traps baited with live Pissodes schwarzi Hopk. males plus pine sections captured 46 female P. schwarzi from I June to 1 September, 1989, indicating the presence of a male-produced sex pheromone. No weevils were captured in unbaited traps, or those baited with females on pine or pine sections alone. Seasonal response of P. schwarzi females to the male-baited pifall traps indicated peak. periods of activity in early June, representing overwintered adults, and mid- to late July, corresponding to the emergence of new adults. Development time of P. schwarzi varied depending on oviposition location on the tree. Overwintered brood adults began to oviposit in May and continued through August

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

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

Infestation Phases and Impacts of Dryocoetes confusus in Subalpine Fir Forests of Southern British Columbia

Subalpine fir mortality and stand decline are increasingly evident in British Columbia (B.C.). This long-term study confirmed Dryocoetes confusus to be the major disturbance agent in high-elevation subalpine forests, killing over two-thirds of subalpine fir in eleven one-hectare study plots. D. confusus infestations in mature stands can be described as early-, mid-, or late-phase. The transition from the early- through late-phase is characterized by a lowered stem density as high levels of D. confusus attack and remove the largest trees, while other mortality factors kill smaller trees. Initially, live subalpine fir density and D. confusus activity varied among plots. By a final assessment, very little difference was observed in live stems per hectare. Mortality from all factors ranged from 0.5% to 5% annually, reaching as high as 80% in-stand mortality with >6 times more dead than live volume. When subalpine fir density was reduced to <400 sph, the D. confusus attack rate declined. Cumulative mortality increased the average gap size in plots from 11 m2 to 18 m2. Our study also showed that D. confusus might be able to switch to a univoltine life cycle, taking advantage of warmer and longer growing seasons that, in part, could explain the rapid increase in mortality in stands

Characterization of Western Spruce Budworm Outbreak Regions in the British Columbia Interior

The western spruce budworm (Choristoneura freemani Razowski; WSB) shapes Douglas-fir (Pseudotsuga menziesii) (Mirb.) Franco forests throughout western North America with periodic, severe landscape-level defoliation events. The largest and most continuous recorded defoliation occurred in the 2000s, largely centered in the Williams Lake and 100 Mile House WSB Outbreak Regions, peaking in 2007 at 847,000 hectares defoliated in B.C. Unique WSB Outbreak Regions in south central B.C. are described using biogeoclimatic ecosystem classification, geography, 106 years of documented defoliation, and 46 stand-level Douglas-fir host tree-ring chronologies. Since the 1980s, recorded defoliation in B.C. has shifted from coastal ecosystems and become a dominant disturbance in drier, colder, Interior Douglas-fir ecosystems. Defoliation records demarcate four outbreaks from 1950-2012 and up to three growth suppression events from 1937- 2012. Outbreak duration was shorter in the north and far south of B.C. with recovery periods (no trees showing growth suppression) shorter over all WSB Outbreak Regions in the 2000s, suggesting trees may be increasingly susceptible to each successive defoliation event. Knowing the regional outbreak periodicity may facilitate early detection of incipient WSB populations, which is critical for management as many of our low elevation Douglas-fir forests become more stressed with changing and unpredictable climate regimes.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author