CHEMICAL ECOLOGY Attraction of Ips pini (Coleoptera: Scolytinae) and Its Predators to Natural Attractants and Synthetic Semiochemicals in Northern California: Implications for Population Monitoring 1, 2 3 2 2 2 4 D. L. DAHLSTEN, D. L. SIX, D. L. ROWNEY, A. B. LAWSON, N. ERBILGIN, AND K. F. RAFFA Environ. Entomol. 33(6): 1554Ð1561 (2004) ABSTRACT Effective management of bark beetles (Coleoptera: Curculionidae, Scolytinae) relies on accurate assessments of pest and predator populations. Semiochemicals provide a powerful tool for attracting bark beetles and associated predators, but the extent to which trap catches reßect actual population densities are poorly understood. We conducted Þeld experiments in California during 2 consecutive yr to determine how attraction of Ips pini (Say) and its major predators to synthetic pheromones vary from each other and from attraction to natural volatiles emitted from colonized hosts. Synthetic lures consisted of different ratios of the (ϩ) and (Ð) enantiomers of ipsdienol, the primary pheromone component of I. pini, with or without lanierone, an additional component that synergizes attraction in some populations. I. pini was consistently attracted to either 3(ϩ)/97(Ϫ) ipsdienol or infested host plant material. Lanierone had no effect on the attraction of I. pini. Coleopteran predators showed a range of responses, more of which coincided with I. pini. Temnochila chlorodia (Mannerheim) (Trogositidae) was attracted to infested host materials and all synthetic lures. Enoclerus lecontei (Wolcott) (Cleridae) preferentially responded to higher ratios of (ϩ)-ipsdienol, and its attraction was strongly enhanced by lanierone. Enoclerus sphegeus F. was most attracted to infested hosts and exhibited a preference for (Ϫ)- over (ϩ)-ipsdienol. Our results suggest that preferences of bark beetles and predators for bark beetle pheromones at the regional scale should be considered before deploying semiochemicals. These results are also consistent with a model of co-evolving responses to pheromones by predators and their prey. The roles of plant volatiles should be further investigated, both to improve monitoring programs and from an ecological perspective. KEY WORDS Temnochila chlorodia, Enoclerus lecontei, Enoclerus sphegeus, biological control, chem- ical ecology BARK BEETLES (Coleoptera: Curculionidae, Scolytinae) Several management tactics are available for reduc- colonize the subcortical tissues of trees. Some mem- ing the negative impacts of bark beetles, including bers of the genera Dendroctonus, Ips, and Scolytus silvicultural practices such as thinning (Nebeker and exhibit large population eruptions that cause severe Hodges 1985, Hindmarch and Reid 2001), sanitation- economic losses in North America (Berryman 1982, salvage logging (Gibson 1989), insecticide applica- Wood 1982b). In most species within these genera, tions (Swezey et al. 1982, Gibson and Bennett 1985, adults that have selected potential host trees release McCullough et al. 1998), and the use of behavior- aggregation pheromones that attract both male and modifying compounds (Gray and Borden 1989, Shea female conspeciÞcs, thus initiating a mass attack et al. 1992, Bertram and Paine 1994, Ross and Dater- (Wood 1982a, Vanderwell 1994). Such pheromonal man 1995). However, accurate population monitoring communication within species of conifer-infesting is required for accurate assessment of each of these bark beetles is closely linked to host tree chemistry, tactics. particularly terpenoids (Renwick and Vite´ 1972, Sey- Synthetic semiochemicals, particularly phero- bold 1993, Vanderwell 1994, Byers 1995). mones, are commonly used to monitor bark beetle populations. However, the use of synthetic chemicals is limited by a paucity of information relating catches in traps baited with synthetic lures to actual numbers 1 Deceased. 2 Division of Insect Biology, 201 Wellman Hall, Department of of bark beetles attracted to volatiles released from Environmental Science, Policy and Management, University of Cal- trees under natural attack (Aukema et al. 2000a). ifornia, Berkeley, CA 94720Ð3113. Thus, an explicit objective when developing lures for 3 School of Forestry, University of Montana, Missoula, MT 59812. monitoring bark beetles or their predators should be 4 Corresponding author: 345 Russell Labs, Department of Ento- mology, University of Wisconsin, Madison, WI 53706 (e-mail: the capability for estimating both relative and total [email protected]). population numbers. Estimates of relative abundance 0046-225X/04/1554Ð1561$04.00/0 ᭧ 2004 Entomological Society of America December 2004 DAHLSTEN ET AL.: ATTRACTION OF I. pini AND PREDATORS 1555 of predators to bark beetles could be useful in pre- predominant predator in California, Enoclerus lecontei dicting whether predator populations are sufÞcient to (Wolcott) (Cleridae), was primarily attracted to Wis- suppress bark beetle populations (Reeve 1997), consin I. pini, whereas the predominant predator in whereas estimates of absolute densities are useful in Wisconsin was most attracted to California I. pini. In evaluating bark beetle populations, economic thresh- contrast, I. pini in California and Wisconsin were most olds, and predator functional and numerical re- attracted to local conspeciÞcs. This disparity in re- sponses. sponse to pheromones has been hypothesized to re- Bark beetles exhibit temporal and geographical ßect locally driven semiochemical adaptations and variation in the production of pheromones (Berisford counter-adaptations among the bark beetle and its et al. 1990, Miller et al. 1997). Furthermore, in some predators (Raffa and Dahlsten 1995, Aukema et al. systems, bark beetles and predators differ in their 2000a, b). attraction to various pheromone components and en- We conducted parallel studies in California and antiomeric ratios (Raffa and Klepzig 1989, Herms et al. Wisconsin to determine which synthetic lures attract 1991, Raffa and Dahlsten 1995, Aukema et al. 2000a, b). predators and bark beetles at rates that most accu- These differences can complicate our ability to esti- rately emulate actual arrival rates to natural phero- mate their relative abundance during monitoring, and mone sources. The results of the Wisconsin I. pini therefore, our ability to make population-based man- study are presented in Aukema et al. (2000a). In the agement decisions (Aukema et al. 2000a). current study, we evaluated responses of I. pini and its We studied the pine engraver, Ips pini (Say), and its most common predators to synthetic lures and natural natural enemies in northern California. I. pini is dis- attractants in California. We also compared our results tributed throughout the pine forests of North America with those from Wisconsin to better understand how (Wood 1982b). In the western United States, it typi- regional responses to pheromones by bark beetles and cally attacks stressed trees. An abundance of breeding their natural enemies can be used to improve the material such as slash generated during harvest oper- efÞcacy of monitoring programs. ations can lead to large population increases and sub- sequent damage to live trees, including the killing of Materials and Methods young trees, top-killing of mature trees, and group killing of large trees (Livingston 1979). Experimental Design and Procedure. A Þeld exper- On entering a suitable host, adult male I. pini emit iment was conducted in mixed Pinus ponderosa Dougl. a terpenoid pheromone, ipsdienol (2-methyl-6-meth- and Pinus jeffreyi Grev. and Balf. forests in Lassen ylene-2,7-octadien-4-ol), which attracts conspeciÞc National Forest, Lassen Co., CA. Study sites were males and females (Birch et al. 1980, Wood 1982a). located in the Blacks Mountain Experimental Forest at Geographically separated populations vary in their Paterson Flat (40Њ44.96Ј N, 121Њ09.30Ј W) in 1997, and production of, and response to, different stereo- located near Poison Lake (40Њ41.00Ј N, 121Њ12.93Ј W) isomers of ipsdienol and the synergist lanierone and Jelly Camp (40Њ47.08Ј N, 121Њ16.25ЈW) in 1998. (2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one) Nine treatments were evaluated in a behavioral choice (Lanier et al. 1980, Teale et al. 1991, Seybold et al. 1992, assay: three enantiomeric ratios (ϩ)/(-) of ipsdienol 1995, Miller et al. 1997). In general, western U.S. pop- (75:25, 50:50, 3:97), with or without lanierone, a ulations are highly attracted to (Ð)-ipsdienol, whereas screened log infested with I. pini, a screened unin- eastern and midwestern populations are more strongly fested log, and an unbaited control. Synthetic lures attracted to 50:50 and 75:25% blends of (ϩ)- to (Ϫ)- were obtained from Phero Tech (Delta, British Co- ipsdienol (Birch et al. 1980, Lanier et al. 1980, Raffa lumbia, Canada), and the release rates were 110 and and Klepzig 1989, Teale and Lanier 1991, Seybold et al. 10 ␮g/d for ipsdienol and lanierone, respectively, at 1995, Aukema et al. 2000a, b). Lanierone seems to be 25ЊC. more biologically active in eastern than western pop- Ips pini males were reared from Þeld-collected slash ulations of I. pini (Teale et al. 1991, Seybold et al. 1992, placed in rearing cans (Raffa and Dahlsten 1995). To Miller et al. 1997, Aukema and Raffa 2000). initiate infestation of treatment bolts, 20 holes, 0.5 cm The phenologies of predator populations are diameter each, were drilled into the phloem of freshly often synchronous with those of their primary hosts cut P. jeffreyi logs, and one male was inserted into each (Schroeder 1996,