Until recently, little was known about the production and use of semiochemicals by cerambycid beetles for intraspecific and possibly interspecific communication (Allison et al. Reference Allison, Borden and Seybold2004). Historically, attractants used for trapping cerambycids have included volatiles associated with larval host plants, such as ethanol, turpentine, and α-pinene, or various fermented sugar baits (e.g., see Champlain and Kirk Reference Champlain and Kirk1932; Phillips et al. Reference Phillips, Wilkening, Atkinson, Nation, Wilkinson and Foltz1988). However, the situation has been changing rapidly over the past decade, with pheromones or related attractants identified for ∼100 cerambycid species since 2004 (e.g., Allison et al. Reference Allison, Borden and Seybold2004; Silk et al. Reference Silk, Sweeney, Wu, Price, Gutowski and Kettela2007; Millar et al. Reference Millar, Hanks, Moreira, Barbour and Lacey2009; Barbour et al. Reference Barbour, Millar, Rodstein, Ray, Alston and Rejzek2011).

In addition, better and more specific baits have been developed for a few cerambycid species based on the observation that they are cross-attracted to bark-beetle semiochemicals. Cross-attraction could be adaptive for cerambycids because their larvae feed on larvae of bark beetles and also because bark-beetle pheromones could advertise a suitable host material (e.g., Allison et al. Reference Allison, Borden and Seybold2003, Reference Allison, Morewood, Borden, Hein and Wilson2004). For example, Miller et al. (Reference Miller, Asaro, Crowe and Duerr2011) attracted large numbers of Monochamus scutellatus (Say), Monochamus titillator (Fabricius), and two other lamiine species, Acanthocinus obsoletus (Olivier) and Acanthocinus nodosus (Fabricius), in the southeastern United States, using a mixture of ethanol, α-pinene, ipsenol, and ipsdienol. In similar work in Spain, Ibeas et al. (Reference Ibeas, Gallego, Diez and Pajares2006) demonstrated that a mixture of α-pinene, ipsenol, and 2-methyl-3-buten-2-ol can be used as a practical management tool for Monochamus galloprovincialis (Olivier). This work was followed up by a search for possible pheromones for M. galloprovincialis by Pajares et al. (Reference Pajares, Alvarez, Ibeas, Gallego, Hall and Farman2010), who found that males produced 2-undecyloxy-1-ethanol (henceforth monochamol). This compound, in combination with host volatiles, was shown to attract beetles of both sexes under laboratory and field conditions, providing the first identification of a pheromone for beetles in the genus Monochamus Dejean (Pajares et al. Reference Pajares, Alvarez, Ibeas, Gallego, Hall and Farman2010).

More recently, Teale et al. (Reference Teale, Wickham, Zhang, Su, Chen and Xiao2011) demonstrated that monochamol appeared to be the sole aggregation pheromone component for another Monochamus species, the Japanese pine sawyer, Monochamus alternatus Hope, with both sexes being attracted. The use of monochamol as a pheromone by two congeneric species is consistent with other recent studies that have shown that pheromone structures often are highly conserved within the Cerambycidae, with species in the same genus, tribe, or subfamily frequently using the same pheromone components (e.g., Hanks et al. Reference Hanks, Millar, Moreira, Barbour, Lacey and McElfresh2007; Silk et al. Reference Silk, Sweeney, Wu, Price, Gutowski and Kettela2007; Barbour et al. Reference Barbour, Millar, Rodstein, Ray, Alston and Rejzek2011; Mitchell et al. Reference Mitchell, Graham, Wong, Reagel, Striman and Hughes2011). We therefore tested the hypothesis that monochamol is an attractant and possible pheromone component for other Monochamus species. Here, we report the results from field bioassays of monochamol in combination with blends of bark-beetle semiochemicals and host volatiles, conducted in a conifer forest in southern British Columbia, Canada.

The experiment was conducted in a forested area dominated by Ponderosa pine, Pinus ponderosa Lawson and Lawson (Pinaceae), ∼3.5 km south of Princeton (49°25′49.99′′N, 120°29′40.70′′W), British Columbia, Canada. Trapping occurred from 6 August–26 September 2011, using multiple-funnel traps (Synergy Semiochemicals Corp., Burnaby, British Columbia, Canada). Monochamol (98% pure), ipsenol (93% pure), and ipsdienol (93% pure) were obtained from Bedoukian Research (Danbury, Connecticut, United States of America). The release devices, produced by Synergy Semiochemicals Corp., included plastic sachets for release of ethanol (10–20 mg/day, 15 ml load per lure), plastic bottles for release of α-pinene (100 mg/day, 15 ml per lure), and bubble caps for release of ipsenol (400 μg/day, 100 mg per lure), ipsdienol (200 μg /day, 100 mg per lure), and monochamol (0.7 mg/day, 95 mg per lure). Trap collection cups contained a killing agent (sections of Ortho^® No-pest^® strips; dichlorvos, The Scotts Miracle-Gro Company, Marysville, Ohio, United States of America). Treatments were as follows: ethanol + α-pinene (plant volatiles control); ethanol + α-pinene + monochamol; ethanol + α-pinene + ipsenol + ipsdienol; and the complete combination of all five components, ethanol + α-pinene + ipsenol + ipsdienol + monochamol.

Four traps were set up in linear transects in each of six blocks (15 m between traps and blocks) and treatments were assigned randomly to traps for a split-plot design with two factors (Steele and Torrie Reference Steele and Torrie1980): treatment (4 levels) and date (3 levels), with a total of six blocks (replicates), respectively. Treatments were re-randomised within blocks three times during the experiment. Insects were collected weekly and. captured insects were not sexed. Cerambycidae classification used in this paper follows Lingafelter (Reference Lingafelter2007).

Differences between treatment means, blocked by site, date, and block, were tested separately for each species using the nonparametric Friedman's Test (PROC FREQ, option CMH; SAS Institute 2001). Differences between pairs of means were tested with the REGWQ means-separation test, which controls for maximum experiment-wise error rates (PROC GLM; SAS Institute 2001). Replicates with fewer than two beetles were dropped from analyses to optimise sample sizes.

Voucher specimens have been deposited in the Spencer Entomological Collection at the Beaty Biodiversity Museum, Vancouver, British Columbia, Canada.

During the course of the experiment, we captured a total of 953 cerambycid beetles of two genera in the subfamily Lamiinae, including 603 Monochamus clamator (LeConte), 63 Monochamus obtusus Casey, 245 M. scutellatus (tribe Monochamini), and 42 Acanthocinus princeps (Walker) (Tribe Acanthocinini). Seventeen Xylotrechus longitarsis Casey (subfamily Cerambycinae) also were captured (too few for statistical analysis).

For all three Monochamus species, traps baited with the combination of monochamol and the host plant volatiles caught significantly more beetles than plant volatiles controls (Fig. 1), whereas the bark-beetle pheromones plus plant volatile treatment was not significantly different than host volatiles controls. The same plant volatiles were found to synergise monochamol for the congener Monochamus carolinensis (Olivier) during a concurrent study run in Illinois, United States of America (Hanks et al. Reference Hanks, Millar, Mongold-Diers, Wong, Meier and Reagel2012). The combination of all five compounds (ethanol, α-pinene, ipsdienol, ipsenol, and monochamol) attracted three times more M. clamator than the plant volatiles + monochamol treatment (Fig. 1), but the bark-beetle pheromones did not enhance attraction of the other two Monochamus species. The fact that the bark-beetle pheromones did not significantly increase attraction of M. scutellatus was inconsistent with the results of earlier studies that had reported that the same compounds greatly increased attraction of both M. scutellatus and M. clamator when combined with ethanol and α-pinene (Allison et al. Reference Allison, Borden, McIntosh, De Groot and Gries2001; Miller et al. Reference Miller, Asaro, Crowe and Duerr2011).

Fig. 1 Mean (±1 SE) number of beetles captured per trap with respect to composition of the lure for three Monochamus and one Acanthocinus species. Means significantly different for Monochamus clamator, Monochamus obtusus, Monochamus scutellatus, and Acanthocinus princeps: Friedman's Q3,72 = 45.7, P < 0.0001; Q3,40 = 14.3, P = 0.0025; Q3,68 = 42.7, P < 0.0001; and Q3,36 = 12.9, P = 0.005, respectively. Means with the same letters within species are not significantly different (REGWQ means-separation test) at P < 0.05.

Acanthocinus princeps showed a different pattern in its response to the treatments, with the greatest numbers being attracted to the plant volatiles plus bark-beetle pheromones treatment (Fig. 1). There was no indication that attraction of this species was affected by monochamol. Synergism between ethanol, α-pinene, and these bark-beetle pheromones has been reported for congeneric species (Miller et al. Reference Miller, Asaro, Crowe and Duerr2011). The lack of attraction of A. princeps to monochamol was consistent with the results of previous field studies in which only Monochamus species, and no other lamiinae species, were attracted to that compound (Pajares et al. Reference Pajares, Alvarez, Ibeas, Gallego, Hall and Farman2010; Teale et al. Reference Teale, Wickham, Zhang, Su, Chen and Xiao2011).

Relatively few of the lamiinae beetles were attracted to traps baited with plant volatiles, despite Monochamus species being reported to be strongly attracted to ethanol and α-pinene (e.g., Miller Reference Miller2006; Costello et al. Reference Costello, Negrón and Jacobi2008). In our studies, the apparent lack of response to plant volatiles that others had shown to attract Monochamus spp. may have been due to competition among traps, such that those baited with both monochamol and plant volatiles drew beetles away from traps baited with plant volatiles alone (e.g., Hanks et al. Reference Hanks, Millar, Mongold-Diers, Wong, Meier and Reagel2012).

In summary, our data strongly supports the hypothesis that monochamol is a common pheromone component shared among Monochamus species. The marked increase in trapping efficiency with baits containing blends of monochamol with host volatiles, coupled with the fact that the pheromone is relatively inexpensive to produce, suggests such baits could be rapidly incorporated into generic surveillance programmes for Monochamus spp.