Nonhost Angiosperm Volatiles and Verbenone Protect Individual Ponderosa Pines from Attack by Western Pine Beetle and Red Turpentine Beetle (Coleoptera: Curculionidae, Scolytinae)

combination with the host monoterpene myrcene is highly attractive to conspecifics (Bedard et al. 1969). Frontalin, produced by male WPB (Kinzer et al. 1969), enhances attraction. Poland et al. (1998) were the first to examine the disruptive effect of NAVs on WPB attraction, but their study was limited in scope to green leaf volatiles only and was conducted at the periphery of the beetle’s native range (Wood 1982). The aldehyde, (E)-2-hexenal, and two alcohols, (E)-2-hexen-1-ol and (Z)-2-hexen-1-ol, significantly reduced numbers of male WPB caught in attractant-baited traps. (Z)-2-hexen-1-ol also reduced numbers of female WPB captured (Poland et al. 1998). Verbenone (4,6,6-trimethylbicyclo[3.1.1]hept-3-en-2-one) is an antiaggregation pheromone of several Dendroctonus spp., including WPB (Borden 1997, Skillen et al. 1997). In 1970, verbenone was shown to elicit a negative response on tethered, flying female WPBs (Hughes and Pitman 1970). Bedard et al. (1980a) showed that verbenone reduced the number of WPB trapped at a baited source. Trap catches were reduced further by higher release rates of verbenone (Bedard et al. 1980a, 1980b; Tilden and Bedard 1988). In a more recent study, verbenone significantly reduced WPB attraction to attractant-baited traps, but no significant difference was observed between 4 and 50 mg/24-hour release rates (Fettig et al. 2005a). It is assumed that verbenone reduces intraspecific competition by reducing crowding of developing brood within the host (Byers et al. 1984). In western North America, the use of verbenone to mitigate bark beetle-caused tree mortality has concentrated on small-scale (i.e., less than 5 ha) stand protection, primarily from MPB infestations in lodgepole pine, Pinus contorta Dougl. ex. Loud, forests (Amman et al. 1989, 1991; Lindgren et al. 1989; Gibson et al. 1991; Shea et al. 1992; Shore et al. 1992; Lindgren and Borden 1993; Progar 2003; Bentz et al. 2005). Results have been favorable but inconsistent at times (Bentz et al. 1989, 2005; Gibson et al. 1991; Progar 2005), which may be caused by, in part, photoisomerization of verbenone to behaviorally inactive chrysanthenone in the presence of UV light (Kostyk et al. 1993) or other factors (Zhang and Schlyter 2004). Verbenone alone does not appear to be effective for reducing WPBcaused tree mortality. For example, the 5-g verbenone pouch (50 mg/24-hour release rate) applied at 125 U/ha was ineffective for protecting ponderosa pine stands from WPB attack in northern California (Fettig 2005). A sprayable formulation of verbenone failed to protect individual ponderosa pines from WPB attack (Gillette et al. 2006). Bertram and Paine (1994) reported that application of ipsdienol and verbenone significantly reduced both numbers of WPB landing on ponderosa pines and the density of attacking beetles. In their study, paired treated and untreated trees were baited with aggregation pheromones to stimulate mass attack, but tree mortality rates were not determined. Lister et al. (1990) reported that verbenone was ineffective for protecting individual ponderosa pines from MPB attack. Fettig et al. (2005a) examined the effect of several bark volatiles (benzyl alcohol, benzaldehyde, trans-conophthorin, guaiacol, nonanal, and salicylaldehyde), green leaf volatiles [(E)-2-hexenal, (E)-2-hexen-1-ol, and (Z)-2-hexen-1-ol], and a blend of these NAVs on WPB attraction in trapping bioassays. The NAV blend did not significantly affect the response of WPB to attractant-baited traps; however, NAV augmented the disruptive effect of 4 and 50 mg/24-hour ( )-verbenone to levels significantly below that of verbenone alone. Additional work revealed that trans-conophthorin was not essential to the efficacy of this blend. The revised NAVV blend [benzyl alcohol, benzaldehyde, guaiacol, nonanal, salicylaldehyde, (E)-2-hexenal, (E)-2-hexen-1-ol, (Z)-2-hexen-1-ol, and verbenone (82%-( ); 50 mg/24-hours)] reduced trap catch by 87% compared with the attractant-baited control. Both males and females were equally affected (Fettig et al. 2005a). The authors suggested that applications of NAVV to ponderosa pine may reduce WPB colonization rates and presumably subsequent levels of tree mortality (Fettig et al. 2005a). Others have shown that blends of NAVs, with or without antiaggregation pheromones, may disrupt aggregation of bark beetles on individual host trees and in forested stands (Wilson et al. 1996, Borden et al. 1998, Huber and Borden 2001, Jakus et al. 2003, Zhang and Schlyter 2004). The effectiveness of NAVs to protect individual trees from WPB attack has not been established but is promising given recent identification of an inhibitory blend in trapping bioassays (Fettig et al. 2005a) and positive results with other coniferophagous bark beetles. The objective of this study was to document the efficacy of NAVV to protect individual ponderosa pines from attack by WPB and RTB.