For. Sci. 60(2):308–316 FUNDAMENTAL RESEARCH http://dx.doi.org/10.5849/forsci.12-092 Copyright © 2014 Society of American Foresters entomology & pathology Influence of Climatic Conditions and Elevation on the Spatial Distribution and Abundance of Trypodendron ambrosia Beetles (Coleoptera: Curculionidae: Scolytinae) in Alaska Robin M. Reich, John E. Lundquist, and Robert E. Acciavatti The objective of this study was to model the influence of temperature and precipitation on the distribution and abundance of the ambrosia beetles in the genus Trypodendron. Although these beetles do not attack and kill healthy trees, their gallery holes and accompanying black and gray stain associated with symbiotic ambrosial fungi can cause significant economic losses to commercial logs and wood products. Beetles were collected along a 1,100-km latitudinal transect 4 times at 2-week intervals at 43 sites beginning early July using Lindgren-funnel traps baited with ethanol, alpha-pinene, and lineatin. Average annual temperature and precipitation were used to partition the state into 25 climatic zones. Large-scale patterns of beetle distribution were correlated with elevation and the temperature and precipitation zones. Results indicate that reasonably accurate predictions of beetle abundance can be generated using models based on trap data collected across several climate zones. Predictions derived from this latitudinal transect can be extrapolated to more remote areas using species–environment relationships based on temperature and precipitation combinations. Partitioning large geographic areas using climatic zones offers a logical approach for predicting insect activity in remote areas, and if implemented on a long-term basis would be able to provide estimates of yearly and seasonal trends in the infestation. Such information would allow forest managers to evaluate the impact on forest ecosystem services and improve future assessments that predict the influence of a changing climate on insect pest migrations and their intensification during outbreaks. Keywords: aerial survey, negative binomial regression, pest survey, spatial pest models hanges in temperature, precipitation, and other climatic Within the forests of this state, insects will probably be among the conditions are often reflected as changes in insect commu- first responders to varying climate and could serve as early bioindi- Cnities (Berryman 1986). Danks (1992) lists several ways cators of climate change. Many believe an “unprecedented” increase that climatic conditions can change insect communities: alterations in forest disturbances in Alaska as a result of climate change has in ecological roles and interactions; changes in insect assemblages, already occurred (Berman et al. 1999), that these changes will likely northern migrations; changing timing of life history events; and continue, and that their effects will cascade across many ecosystems. increase or decrease in host defense chemicals. In Alaska, both tem- As one travels northward across Alaska from the south coast, perature and precipitation show geographic patterns that are influ- growing seasons get shorter, winters get more extreme, and springs enced and often determined by the local and regional geography, come later and are cooler. Along this transect, different insect species and both can change with time. The distribution and abundance of exhibit varying patterns of distribution and abundance. In a recent different insect species in Alaska vary greatly among locations with forest pest survey, various insect pests were sampled with traps in differing climatic conditions (Werner 2007). stands of spruce located at various locations from Seward in south Effects of a changing climate are expected to be greatest in the central Alaska to the geographic limit of spruce trees at the southern northern latitudes (Stocks 2004). Because of its unique geographic foot of the Brooks Range in the north (Lamb and Wurtz 2008). position at the northern edge of various forest types, Alaska has been Observations made during this survey noted that Trypodendron am- referred to as the “poster state for global warming” (Weise 2006). brosia beetles were the most abundant and most widespread of all Manuscript received August 3, 2012; accepted June 25, 2013; published online August 8, 2013. Affiliations: Robin M. Reich ([email protected]), Colorado State University. John E. Lundquist ([email protected]), USDA Forest Service, Anchorage, AK. Robert E. Acciavatti ([email protected]), Carnegie Museum of Natural History. Acknowledgments: We wish to thank Rick Kelsey, Yu Wei, and Ashley Steele for reviewing and editing earlier versions of this manuscript. This study was funded in part by the Western Wildland Environmental Threat Assessment Center. 308 Forest Science • April 2014 the insect species trapped and that their abundance varied through- southern slopes of the Brooks Range (latitude 68oN) in the north, a out the summer. Numbers trapped varied among different geo- distance of around 1,100 km. Sites were located using a systematic graphic regions with greater numbers occurring in the southern unaligned sample design that combines features of both simple ran- latitudes. Three Trypodendron species were identified: Trypodendron dom and systematic sampling. With this design, the 1,100-km tran- lineatum (Oliver), T. betulae (Swaine), and T. retusum (LeConte). sect was divided into 13 sections of varying lengths, and within each Based on published records and specimen data in the USDA Forest section 3 sites were randomly located for a total of 43 sites; two Service reference collections at Anchorage and Juneau, the most sections had only two sites. The length of the sections varied on the common Trypodendron species in Alaska is T. lineatum, the striped basis of ease of accessibility, presence of spruce forest types, and ambrosia beetle (Sikes 2009). The preferred hosts of T. lineatum are ownership (federal or state lands). Plots were located that visually white spruce (Picea glauca (Mill.) B.S.P.), Sitka spruce (Picea sitch- compared to photo series AKHD 07 to AKHD 11 in Ottmar and ensis (Bong.) Carr.), Lutz spruce (Picea lutzii Little), and western Vihnanek (2002). Specifically, sites were placed in stands of mixed hemlock (Tsuga heterophylla (Raf.) Sarg.) (Bright and Stark 1973, hardwood (primarily paper birch, Betula papyrifera Marshall) and Bright 1976, Furniss et al. 2002, Holsten et al. 2009). conifer, where white spruce was codominant or slightly emerging as Trypodendron ambrosia beetles are a group of small (around 4 dominant and represented 10–40% of the overstory. The distance mm) beetles whose larvae feed on fungi cultured by adults within the between sample sites within a section ranged from 0.1 km to 19 km, wood they infest. Adult T. lineatum beetles emerge from overwin- with an average distance of 2.3 km. All sample sites were georefer- tering sites in the forest floor duff layer during the spring when enced using a global positioning system unit (Garmin global posi- temperatures reach 15.5° C to 18.3° C (Lindgren 1990). The tioning systems (GPS) map 76CSx). emerging adults are attracted to recently dead or dying trees where mating occurs. The female tunnels through the bark into the wood to lay its eggs. Symbiotic fungi, introduced to the galleries by the Geographic Information System (GIS) Layers boring insects as a source of food for their larvae, give the name Raster layers representing the average monthly temperatures “ambrosia” to this type of Scolytinae beetle. These fungi grow and (° C) and precipitation (mm) for the state of Alaska were obtained fruit within the galleries where they stain the wood black/gray. Six to from the USGS Alaska Science Center, High Altitude Climate 8 weeks after eggs are laid, young adults emerge from the original Transects1 with a 1,000-m spatial resolution for use in a GIS. These holes created by their parents, and these disperse to overwintering layers were used to identify five temperature zones and five precip- sites in the forest floor. Except for a few hours once each generation itation zones in combinations that defined 25 unique climatic zones during which time the dispersal flight takes place, these insects live (Figure 1; Reich et al. 2008). The climate zones were based on a entirely within the host tree. histogram equalization approach that produced a uniform distribu- In previous years, when logging and timber production were tion of temperatures and precipitations across the state of Alaska more prevalent, the wood stain caused by ambrosia beetles resulted (Acharya and Ray 2005; Table 1). Zonal statistics were used to in significant economic losses to commercial conifer logs in Alaska summarize the variability in temperatures and precipitation in each due to timber degrade (Boyce 1961). Although the economic sig- of the 25 climate zones. One of the unique features of this approach nificance of Trypodendron ambrosia beetles has subsided in recent in defining the temperature and precipitation zones was a strong years, their ecological importance as decomposers of stressed, dam- linear correlation between the integers (1, 2, 3, 4, 5) used to repre- aged, and dying conifers is possibly underappreciated. sent the temperature and precipitation zones and the average Because Trypodendron ambrosia beetles infest recently dead or monthly temperature (␳ˆ ϭ 0.99) and average monthly precipita- dying trees, they may be an important indicator of forest health. T tion (␳ˆ ϭ 0.88) characterizing the