Great Basin )Jaturalist 56(4), © 1996, pp. 348-359 WESTERN BALSAM BARK BEETLE, DRYOCOETES CONFUSUS SWAINE, FLIGHT PERIODICITY IN NORTHERN UTAH E. Matthew Hansenl ABSTRACT.-The flight periodicity of western balsam bark beetle (Dryocoetes confusus Swaine) in Big Cottonwood Canyon, Utah, was studied during the summer months of 1992, 1993, and 1994. Contents of baited funnel traps were tallied by species up to 3 times weekly. Two main periods of flight activity were observed each year. The first and, gener­ ally, largest occurred in early summer soon after flight was initiated for the season. A 2nd period was observed in late summer, generally August. Timing of the 2 periods was influenced by unusually warm or cool weather in each study year. The 1st period had more males than females while the 2nd period had a majority of females. Except during periods of cool or wet weather, western balsam bark beetles were found to be active at least at minimal levels from June through September. Key words: Dryocoetes confusus, flight periodicity, Scolytidae, insect control, insect phenology, Abies lasiocarpa, Utah forests. The western balsam bark beetle, Dryocoetes ratios, weather influences, and associated scoly­ confusus Swaine (Coleoptera: Scolytidae), is a tids are also presented. serious insect pest of true firs. This insect's life cycle is not fully understood Qohnson 1985), MATERIALS AND METHODS however, possibly due to the traditionally low commercial value of its host. In British Colum­ Five plots were established on 5-6 June 1992 bia, for example, timber losses from western in Big Cottonwood Canyon, Utah, ranging from balsam bark beetles have only relatively recently 2000 to 2840 m elevation. Plots were selected been calculated (Doidge 1981). The need to from areas of recent beetle activity indicated understand the life cycle and behavior of this by fading or red subalpine fir crowns. bark beetle has increased in relation to the in­ The plot at 2000 m has a white fir (Abies creased commercial and aesthetic value of true concolor [Gord and Glend.] Lindl. ex Hildebr.)J firs. Douglas-fir (Pseudotsuga menziesii [Mirb.] Drought-subjected subalpine fir, Abies lasio­ Franco) mix and also had the least amount of carpa (Hook.) Nutt., in northern Utah has been fading host material of any plot. This is gener­ experiencing a western balsam bark beetle out­ ally the lower elevational band for subalpine fir break that began in 1989. Most of the affected in Big Cottonwood Canyon. Small amounts of trees are on the heavily visited Wasatch-Cache subalpine fir can be found immediately uphill National Forest, including the canyons east of from the plot. The higher plots are dominated Salt Lake City where picnic areas, campgrounds, by subalpine fir, sometimes in association with and ski resorts are common. This caused local Douglas-fir, quaking aspen (Populus tremuloides forest managers to seek beetle abatement mea­ Michx.), or Engelmann spruce (Picea engel­ sures. Bark beetle control strategies, such as de­ mannii Parry ex Engelm.). ployment of semiochemicals or cultural treat­ Each plot contained three 16-unit Lindgren ments, require knowledge of the time frame in funnel traps2 spaced at about 50-m intervals in which beetles emerge from infested host mate­ a triangular pattern. Traps were baited with a rial to attack new hosts. This is a report of 3 yr semiochemical mixture containing exo-brevi­ of western balsam bark beetle flight periodicity comin (racemic) released at 1 mg/24 h at 24°C3 data from Big Cottonwood Canyon, Utah. Sex (Borden et al. 1987). Traps were hung as high lUSDA Forest Service, Intem10untain Research Station, 860 North 1200 East, Logan, UT 8432l. 2Phero Tech Inc., Delta, B.C., Canada. 3Phero Tech Inc., Delta, B.C., Canada. 348 1996] DRYOCOETES CONFUSUS FLIGHT PERIODICITY 349 as possible on branches, leaving the trap cup at 2600/2660 m and 2840 m (this station is geo­ about 1.5 m aboveground. Trap cups were graphically and elevationally between the 2 emptied up to 3 times weekly to reduce losses plots). Daily maximum/minimum temperatures to predation. Cups were emptied less frequently and daily precipitation were plotted from 20 late in each study year as captures diminished. May through 31 October for each study year. Western balsam bark beetles were tallied along with associated scolytids and important preda­ RESULTS tors, namely checkered beetles (Enoclerus spp.). Flight Periodicity Identification of associated scolytids was pro­ vided by Stephen L. Wood4. D. confusus cap­ 1750 METERs.-This site was used only in tures for the entire season were then totaled 1993 with a total of 42 D. confusus captures. for each plot. The percentage of the annual Consequently, I deleted it from consideration total caught at each observation was then plot­ for the purpose of this study. Nearby white fir ted against date for each location. mortality that was examined contained evi­ The study was repeated starting in mid-May dence only of fir engraver beetle, Scolytus ven­ 1993 with 5 plots installed from 1750 to 2840 tralis LeConte. m elevation. Two sites from 1992 were reused, 2000 METERs.-Because this site had rela­ 2 were moved a short distance (about 100 m tively few captures, I used it only in 1992. horizontal), and 1 was new. The lowest eleva­ Flight activity for that year sharply peaked in tion plot was deliberately established in the mid- to late June (Fig. 1). A substantially smaller white fir zone. Low-elevation plots were in­ surge occurred in early August. D. confusus stalled earlier in the year than in 1992 to ensure captures totaled 1469. The 1st wave of activity placement before beetle flight commenced. accounted for 84% of total captures. Plots at 1750 and 2350 m were installed 25 2310/2350 METERs.-The substantial num­ May 1993, and the plot at 2560 m was estab­ ber of captures at the first observation of 8 lished 27 May 1993. The plot at 2660 m was June 1992 indicates that flight was likely initi­ installed on 8 June 1993 and the plot at 2840 m ated before plot establishment (Fig. 2). Cap­ on 21 June 1993. tures peaked in mid-June with activity contin­ The 1994 flight periodicity study utilized uing throughout the month. A 2nd surge began the 4 highest sites from 1992, ranging in eleva­ in mid-July and tapered off in mid-August. D. tion from 2310 to 2840 m. These areas contin­ confusus captures totaled 19,071. Forty-one ued to contain fading host material throughout percent of the total occurred in the 1st surge. each study year. The low-elevation sites, lacking In 1993 traps at this plot began to capture a substantial subalpine fir component, were beetles in mid-June with a small peak occurring dropped from the study due to the small popu­ in late June. A 2nd wave of captures began in lations of D. confusus in those areas. The plot late July, peaking in mid- to late August. D. at 2310 m was established on 10 May 1994, confusus captures were about 9% of those in while the remaining plots were installed on 25 1992, totaling 1800. The 1st wave of captures May 1994. This gives 3 consecutive years of accounted for 10% of the total. flight period data for 4 locations. Capture patterns of 1994 were very similar The first 10 D. confusus from each trap cup to those of 1992. The first positive observation observation, totaling 30 per plot, were tallied for was on 3 June 1994. An early summer peak sex in 1993 and 1994. Females were identified occurred on 13 June 1994 with activity taper­ by a prominent setal brush on the frons (Borden ing off in late June through early July. A late­ et al. 1987). For 1993 and 1994 the sex ratio of summer surge occurred in mid- to late July with each distinct flight surge was compared. The captures gradually diminishing through early division between surges was determined from October. D. confusus captures totaled 2574, each significant flight activity lapse not associ­ with 30% caught in the 1st surge. ated with cool or wet weather. 2560 METERs.-The first 1992 observation Weather data from Brighton-Silver Lake5 was positive, indicating that flight was possibly was compared with flight activity for the plots initiated before plot establishment. Beetles 4Professor emeritus, Life Science '.luseum and Department of Zoology, Brigham Young l'niversity, Provo, IT '"Salt Lake City \Vatershed .\!anagement. 350 GREAT BASIN NATURALIST [Volume 56 -c 50 -r------------------------------, ~ -5. 40 ~ ~ 30 ~ ~ 20 C ~1:~-·····-·····-·····~···;~··I·l~·····~~III~I~~,~~~,~~ __ ~I ______________~ 20 6/1 15 7/1 15 8/1 15 9/1 15 10/1 15 31 1992 Fig. 1. Percentage of total (/1 = 1469) seasonal Dryocoetes conjilS[lS captures per obsenation at 2000 111, 20 ~Iay-31 October. AITOW indicates the trough between surges not associated with cool or wet weather. -c 20 -r----------------------------, ~ :::l 1i15 +............................................................. : .......................................................................................................................................................................... j ~ (/) ~Q) 10 Q) .a C 5 ~Q) a.. O~---U~~iL~~~~-L~~~~~~~-~--~---- 20 6/1 15 7/1 15 8/1 15 9/1 15 10/1 15 31 1992 u C 5 _. -- ~ Q) ····Il,· a.. o I, ,III IIIII r 20 6/1 15 7/1 15 8/1 15 9/1 15 10/1 15 31 1993 -c 20 .-----------------------------, ~ :::l 1i15 + ..................................................... ·······T··············································............................................................................................................. ················1 ~ (/) ~ 10 + ........................................................... +.................. / Q) Q) .a C 5 ~ Q) a.. o ~ __ ~i--LLl~~iL~~-L~~~~~~~~ __L- __-L ______ ~ 20 6/1 15 7/1 15 8/1 15 9/1 15 10/1 15 31 1994 Fig. 2. Percentage of total (111992 = 19,071, 11199:3 = 1800, 11199 .. = 2574) seasonal Dryocoetes COl1jllSllS captures per obsen'ation at 2310/2350 111, 20 \Iay-31 October.