Chapter 14 Management Strategies for Bark Beetles in Conifer Forests Christopher J. Fettig1 and Jacek Hilszczanskin 2 1Invasives and Threats Team, Pacific Southwest Research Station, USDA Forest Service, Davis, CA, USA, 2Department of Forest Protection, Forest Research Institute, Se˛kocin Stary, Raszyn, Poland 1. INTRODUCTION designed to address current infestations by manipulating Bark beetles (Coleoptera: Curculionidae, Scolytinae) are beetle populations, and often includes the use of fire, insec­ important disturbance agents in conifer forests. The genera ticides, semiochemicals (i.e., chemicals released by one Dendroctonus, Ips,andScolytus are well recognized in this organism that elicit a response, usually behavior, in another regard (Table 14.1). For example, in western North America, organism), sanitation harvests, or a combination of these the mountain pine beetle (Dendroctonus ponderosae treatments. Indirect control is preventive, and designed to Hopkins) colonizes several tree species, most notably lod­ reduce the probability and severity of future bark beetle gepole pine (Pinus contorta Dougl. ex Loud.), ponderosa infestations within treated areas by manipulating stand, pine (Pinus ponderosa Dougl. ex Laws.), and whitebark pine forest, and/or landscape conditions by reducing the number (Pinus albicaulis Engelm.). Recent outbreaks have been of susceptible hosts through thinning, prescribed burning, severe, long lasting, and well documented, with over 27 and altering age classes and species composition. Unlike million hectares impacted (BC Ministry of Forests, Lands direct control, the focus of indirect control is on the suscep­ and Natural Resource Operations, 2012; USDA Forest tibility of residual forest structure and composition to future Service, 2012). In British Columbia, Canada, alone 710 infestations. million m3 of timber have been killed (BC Ministry of The purpose of this chapter is to synthesize information Forests, Lands and Natural Resource Operations, 2012). In related to the management of bark beetles in conifer forests, Europe, the European spruce beetle (Ips typographus (L.)) and to present a case study on the management of I. typo­ is regarded as the most important pest of Norway spruce graphus in central Europe. We concentrate on what some (Picea abies (L.) Karst.) (Christiansen and Bakke, 1988; authors commonly refer to as aggressive species (i.e., they Schelhaas et al.,2003), an indigenous species also widely are capable of causing large amounts of tree mortality during planted for commercial timber production outside its native certain circumstances) (Table 14.1), and draw heavily from range. It is estimated that 8% of all tree mortality that research conducted and practical experience gained while occurred in Europe between 1850 and 2000 was caused by working in North America and Europe. Our hope is that this bark beetles, primarily I. typographus (Schelhaas et al., synthesis provides a basic understanding of current and 2003). In Asia, the red turpentine beetle (Dendroctonus evolving strategies for reducing the negative impacts of bark valens LeConte), an exotic invasive introduced from North beetles on forests. However, we stress that in most cases we America, has caused significant levels of tree mortality since concentrate on native species important to the proper func­ being detected in China in 1998 (Yan et al.,2005). Although tioning of forest ecosystems as they regulate certain aspects considered a minor pest in its native range, more than 10 of primary production, nutrient cycling, and ecological suc­ million Chinese red pine (Pinus tabuliformis Carr.), China’s cession (Romme et al.,1986). In this context, some level of most widely planted pine species, have been killed by tree mortality is desirable and often results in a mosaic of age D. valens. classes and species compositions that increases resilience to Over the last century, substantial basic and applied bark beetles and other disturbances. This differs from the research has been devoted to the development of effective negative impacts associated with outbreaks, which often tools and tactics for mitigating undesirable levels of tree merit intervention. We encourage the reader to delve deeper mortality attributed to bark beetles. There are two basic into the literature cited for more detailed information on spe­ approaches. Direct control involves short-term tactics cific bark beetle–host complexes. Bark Beetles. http://dx.doi.org/10.1016/B978-0-12-417156-5.00014-9 © 2015 Elsevier Inc. All rights reserved. 555 556 Bark Beetles TABLE 14.1 Bark Beetle Species Notable for Causing Substantial Levels of Tree Mortality in Conifer Forests within their Native Ranges Common Name Scientific Name Common Host(s) Arizona fivespined ips Ips lecontei P. ponderosa California fivespined Ips paraconfusus P. contorta, Pinus lambertiana, P. ponderosa ips Douglas-fir beetle Dendroctonus Pseudotsuga menziesii pseudotsugae eastern fivespined ips Ips grandicollis Pinus echinata, Pinus elliottii, Pinus taeda, Pinus virginiana eastern larch beetle Dendroctonus simplex Larix laricina eastern six-spined Ips calligraphus P. echinata, P. elliotti, P. ponderosa, P. taeda, P. virginiana engraver European spruce Ips typographus Pi. abies, Picea orientalis, Picea yezoensis, occasionally Pinus sylvestris beetle fir engraver Scolytus ventralis Abies concolor, Abies grandis, Abies magnifica Jeffrey pine beetle Dendroctonus jeffreyi Pinus jeffreyi larger Mexican pine Dendroctonus P. ponderosa beetle approximatus mountain pine beetle Dendroctonus P. albicaulis, P. contorta, Pinus flexilis, P. lambertiana, Pinus monticola, P. ponderosae ponderosa northern spruce Ips perturbatus Picea glauca, Picea x lutzii engraver pine engraver Ips pini P. contorta, P. jeffreyi, P. lambertiana, P. ponderosa, Pinus resinosa pinyon ips Ips confusus Pinus edulis, Pinus monophylla roundheaded pine Dendroctonus Pinus arizonica, Pinus engelmannii, P. flexilis, Pinus leiophylla, P. ponderosa, beetle adjunctus Pinus strobiformis six-toothed bark Ips sexdentatus Pinus heldreichii, Pinus nigra, Pinus pinaster, P. sylvestris, Pi. orientalis beetle southern pine beetle Dendroctonus frontalis P. echinata, P. engelmannii, P. leiophylla, P. ponderosa, Pinus rigida, P. taeda, P. virginiana spruce beetle Dendroctonus micans P. sylvestris, Pi. abies spruce beetle Dendroctonus Picea engelmannii, Pi. glauca, Picea pungens, Picea sitchensis rufipennis western balsam bark Dryocoetes confusus Abies lasiocarpa beetle western pine beetle Dendroctonus Pinus coulteri, P. ponderosa brevicomis 1.1 Bark Beetle Ecology therefore must detect and locate the correct habitat, correct Some knowledge of bark beetle ecology and physiology is tree species, and the most susceptible trees within these important to understanding the utility and proper implemen­ species with efficiency (Byers, 1995; Borden, 1997; tation of control strategies. In brief, adult bark beetles Schlyter and Birgersson, 1999). For example, the dominant maintain limited energy reserves (Atkins, 1966), and are theory of host finding and selection in D. ponderosae sug­ highly susceptible to predation, starvation, and adverse gests pioneering females use a combination of random weather conditions when searching for hosts. Beetles landings and visual orientations followed by direct Management Strategies for Bark Beetles in Conifer Forests Chapter 14 557 assessment of hosts based on olfactory and/or gustatory cues (Raffa and Berryman, 1982, 1983; Wood, 1982). Given the cues received during this process and other factors, such as the beetle’s internal physiology (Wallin and Raffa, 2000), the host is either rejected or accepted. If the host is accepted, gallery construction is initiated upon which many species release aggregation pheromones that enhance attraction of conspecifics to the target tree (Borden, 1985; Byers, 1995; Zhang and Schlyter, 2004) as successful colonization requires overcoming host tree defenses (Wood, 1972; Hodges et al., 1979, 1985; Raffa et al., 1993; Franceschi et al., 2005). This can only be accomplished by recruitment of a critical minimum number of beetles to mass attack the tree and overwhelm its defenses. Most conifers are capable of mobilizing large amounts FIGURE 14.1 Beetles that initiate host colonization are often killed by of oleoresin following wounding, which constitutes their drowning or immobilization in resin when hosts are vigorous, as depicted primary defense against bark beetle attack (Vite´, 1961, by this Dendroctonus brevicomis. This is usually considered the primary defense of conifers against bark beetle attack. Management strategies exist Reid et al., 1967, Franceschi et al., 2005) (see to increase tree vigor, and thus reduce the susceptibility of trees and forests Chapter 5); however, resin chemistry also plays an to bark beetles. Photo credit: C. Fettig, Pacific Southwest Research important role (Smith, 1966; Cook and Hain, 1988; Reid Station, USDA Forest Service. and Purcell, 2011). The development of a hypersensitive response, consisting mainly of secondary metabolites States to reduce the risk, severity, and extent of wildfires around points of attack, has also been demonstrated to be (Stephens et al., 2012). However, much of the biomass important (Lieutier, 2004). Beetles that initiate host removed is unmerchantable, and therefore cut and lopped selection are often killed by drowning or immobilization (i.e., the boles are severed into short lengths and limbs in resin (termed pitch out) especially when