National programs to detect nonnative species of insects, particularly bark and woodboring beetles (Coleoptera), are common around the world due to global movement of goods (Brockerhoff et al. 2006, Brockerhoff and Liebhold 2017, Poland and Rassati 2019, Rabaglia et al. 2019, Aguirre Gil et al. 2021, Thurston et al. 2022). Combining lures for different species of bark and woodboring beetles can help reduce the costs of detection programs for nonnative species (Hanks et al. 2012, Miller et al. 2015, Fan et al. 2019, Poland and Rassati 2019, Rice et al. 2020). In the southeastern United States, adding α-pinene (a common volatile released from pines) lures to traps baited with ethanol (a known attractant for ambrosia beetles) lures results in a lure blend that is broadly attractive to bark and ambrosia beetles, with minimal interruption in attraction of ambrosia beetles due to the addition of α-pinene (Miller and Rabaglia 2009). The combination is also attractive to several species of longhorn beetles (Cerambycidae) and reproduction weevils (Curculionidae) (Miller 2006).

The bark beetle pheromones ipsdienol and ipsenol are used as pheromones by three common species of Ips in the Southeast and are attractive to all three species when used in combination (Miller et al. 2005, Allison et al. 2012a). Traps baited with ipsenol + ipsdienol are also attractive to numerous species of woodborers, predators, and fungivores (Miller and Asaro 2005, Allison et al. 2013). Adding the binary blend of ipsdienol + ipsenol to the binary blend of ethanol + α-pinene enhanced the abundance and diversity of species captured in the Southeast (Miller et al. 2011).

The benefits of retaining both ethanol and α-pinene in the quaternary blend were verified in Georgia (Miller 2020). However, the individual effects of ipsdienol and ipsenol on catches of bark and woodboring beetles to traps baited with ethanol + α-pinene are unknown. Therefore, my objective was to evaluate the benefit of retaining ipsdienol and/or ipsenol as part of a generic trap lure blend with ethanol + α-pinene to maximize the diversity and abundance of bark and woodboring beetles captured in the southeastern United States.

Materials and Methods

In 2007, I conducted a trapping study (30 May–2 August 2007) in a mature stand of loblolly pine, Pinus taeda (L.) (33.392°N, 83.377°W) on the Oconee National Forest near Eatonton, GA. The stand had experienced a prescribed burn in February 2007. Ethanol and α-pinene (enantiomeric purity > 95% [–]) pouch lures were obtained from Pherotech International (Delta, British Columbia, Canada). The release rates of ethanol and α-pinene from the pouch lures were 0.6 g/day and 0.1–0.6 g/day, respectively, at 25–28°C (determined by the manufacturer). Bubblecap lures containing racemic ipsdienol and racemic ipsenol were obtained from Synergy Semiochemicals Inc. (Burnaby, British Columbia, Canada). The release rates of ipsdienol and ipsenol from the bubblecap lures were 0.1–0.2 mg/day and 0.2–0.3 mg/day, respectively, at 25°C (determined by the manufacturer).

Forty, 8-unit multiple-funnel traps (Synergy Semiochemicals Inc.) were deployed in a randomized complete block design with 10 replicate blocks of four traps/block. Traps were hung on twine strung between trees such that the collection cup of each trap was approximately 0.5 m above ground level and each trap was ≥2 m from any tree. Traps within a block were spaced 8–12 m apart whereas blocks were spaced 10–20 m apart. In each block, one of the following four lure treatments was randomly allocated to each trap: (1) ethanol + α-pinene (EA); (2) EA + ipsdienol; (3) EA + ipsenol; and (4) EA + ipsdienol + ipsenol. Approximately 150 ml of an aqueous solution of propylene glycol (Peak RV & Marine Antifreeze, Old World Industries Inc., Northbrook, IL, USA) was added to each collection cup to kill and preserve beetles captured (Miller and Duerr 2008). Fresh propylene glycol solution was added to collection cups after each 2-wk collection event. Voucher specimens were deposited at the University of Georgia Collection of Arthropods, Athens, GA.

Trap catch data were analyzed with the SYSTAT (ver. 13) and SigmaStat (ver. 3.01) statistical packages (SYSTAT Software Inc., Point Richmond, CA) for species caught in sufficient numbers (n ≥ 30). Data were transformed by ln(Y+1) as needed to ensure normality and homoscedasticity (Pepper et al. 1997) and verified by the Shapiro-Wilk and Equal Variance tests, respectively. In all analyses, I employed a mixed-model analysis of variance (ANOVA) (y = ipsdienol + ipsenol + ipsdienol * ipsenol + block + error) with block as a random factor. Comparisons of mean treatment catches were conducted with the Holm-Sidak multiple comparison test, which controls the experiment-wise error rate at 0.05 (Glantz 2005).

Results

A total of 23,531 forest-dwelling beetles were captured in the study, representing 10 families of bark and woodboring beetles and associated species of predators and fungivores (Table 1). At least one species was caught in sufficient numbers in each family for analyses. The most abundant and diverse families were Cerambycidae and Curculionidae.

Table 1 Total catches of beetles in traps baited with ethanol + a-pinene (EA), with or without ipsenol (S) and/or ipsdienol (D), in northcentral Georgia in 2007 (n = 10). (—) indicates none captured.

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Table 1 Continued.

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Six species of Cerambycidae were captured in sufficient numbers for analyses (Table 1). Catches of Acanthocinus obsoletus (Olivier) and Monochamus titillator (F.) were affected by both ipsdienol and ipsenol, with significant interaction between the two factors (Table 2). Catches of both species in traps baited with ethanol + α-pinene were increased by the addition of either ipsdienol or ipsenol (Table 3). However, there was no significant increase in catches in traps baited with both compounds compared to traps baited with each compound individually. Catches of the woodborers Buprestis lineata F. (Buprestidae), Acanthocinus nodosus (F.), Arhopalus rusticus (L.), Neoclytus scutellaris (Olivier), Xylotrechus sagittatus (Germar) (Cerambycidae), and Alaus myops (F.) (Elateridae) were unaffected by ipsdienol and ipsenol lure treatments (Table 4).

Table 2 ANOVA table for effects of ipsdienol (D), ipsenol (S), and the interaction between the two treatments (D × S) on catches of beetles in traps baited with ethanol + a-pinene northcentral Georgia in 2007.

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Table 3 Mean (±SE) catches of beetles in traps baited with ethanol + a-pinene (EA), with or without ipsenol (S) and/or ipsdienol (D), in northcentral Georgia in 2007 (n = 10).* (—) indicates none captured.

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Table 4 Mean (±SE) catches, and F and P values (ANOVA) for beetle species not affected by the lure treatments (ipsdienol and/or ipsenol) in northcentral Georgia in 2007 (n = 10).

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Sufficient numbers of 16 species of Curculionidae were caught in the study for analyses (Table 1). Catches of the bark beetles Ips avulsus (Eichhoff), Ips calligraphus (Germar), and Orthotomicus caelatus (Eichhoff) in traps baited with ethanol+α-pinene were affected by both ipsdienol and ipsenol, whereas catches of Ips grandicollis (Eichhoff) were only affected by ipsenol; the interaction term was only significant for O. caelatus (Table 2). Traps baited with ipsdienol + ipsenol caught the most I. avulsus; the lowest numbers were in traps not baited with either compound (Table 3). Ips grandicollis was attracted equally to traps baited with ipsenol or ipsdienol + ipsenol. Catches of I. calligraphus were greatest in traps baited with ipsdienol or ipsenol+ipsdienol and lowest in traps not baited with either compound (Table 3). Only traps baited with ipsdienol alone caught significant numbers of O. caelatus; the addition of ipsenol to traps baited with ethanol + α-pinene interrupted attraction to ipsdienol (Table 3).

Ipsdienol and the interaction between ipsdienol and ipsenol affected catches of the bark beetle Hylastes salebrosus Eichhoff. Catches of H. salebrosus were lower in traps baited with both ipsdienol and ipsenol than in traps baited each compound individually (Table 3). Lure treatments had no effect on catches of the bark beetles Dendroctonus terebrans (Olivier) and Hylastes tenuis Eichhoff (Table 4). Similarly, ipsenol and ipsdienol lure treatments had no effect on catches of the ambrosia beetles Dryoxylon onoharaense Murayama, Monarthrum fasciatum (Say), Monarthrum mali (Fitch), Xyleborinus saxesenii (Ratzeburg), and Xylosandrus crassiusculus (Motschulsky), and the snout weevils Dryophthorus americanus Bedel, Hylobius pales Herbst, Pachylobius picivorus (Germar), and Stenoscelis brevis (Boheman) (Curculionidae) (Table 4).

Species in five families of predators were affected by lure treatments. Catches of Thanasimus dubius (F.) (Cleridae) were affected by ipsdienol and the interaction between ipsdienol and ipsenol (Table 2). Catches in traps baited with ipsdienol caught the most T. dubius with the addition of ipsenol interrupting attraction (Table 3). In contrast, ipsenol and the interaction between ipsdienol and ipsenol affected catches of Platysoma spp. (Histeridae) (Table 2) with catches greatest in traps baited with ipsenol and lowest in those not baited with either ipsdienol or ipsenol (Table 3). The addition of ipsdienol to traps baited with ethanol + α-pinene increased catches of Platysoma spp. but decreased catches in traps baited with ethanol + α-pinene + ipsenol.

Catches of the predators Temnoscheila virescens (F.) (Trogossitidae) and Lasconotus spp. (Zopheridae) were affected by all three model factors (Table 2). Trap catches of T. virescens in traps baited with ethanol + α-pinene increased with the addition of either ipsdienol or ipsenol (Table 3). There was no significant increase in catches in traps baited with both compounds compared to traps baited with each ipsdienol or ipsenol separately. In contrast, catches of Lasconotus spp. occurred in traps baited with ipsenol + ipsdienol negating attraction (Table 3). There was a significant effect of lure treatments on catches of the predator Aulonium tuberculatum LeConte (Zopheridae) (F_2,18 = 8.530, P= 0.002); none were caught in traps baited solely with ethanol + α-pinene (Table 1). Catches were greatest in traps baited with ipsenol or ipsdienol + ipsenol (Table 3). There was no lure effect on catches of the predators Tenebroides spp. (Trogossitidae) and the fungivore Pycnomerus sulcicollis LeConte (Zopheridae) (Table 4).

Discussion

The objective of lure combinations in detection programs for bark and woodboring beetles and associated species is to detect the maximum number of species. The abundance of some species can be enhanced by various combinations, whereas others may be reduced. In assessing the trade-off, managers should retain lure combinations that satisfy their objectives in a detection program. Abundance for these species in traps is likely associated with the likelihood of detecting those species when population numbers are low.

The answer to the question of retaining ipsdienol and/or ipsenol in a generic pine beetle blend is unclear from the current study. Decisions by managers will likely depend on target groups for their programs. For example, with bark beetles, only catches of I. avulsus benefited from both compounds being added to the blend (Table 3). Results were mixed for the other four species of bark beetles. Catches of three species were lower in traps baited with both ipsdienol and ipsenol than in traps baited with the compounds individually. Catches of three other species of bark beetles, two species of reproduction weevils, and five species of ambrosia beetles in traps baited with ethanol+α-pinene were not adversely affected by ipsdienol and/or ipsenol (Table 4). To maximize detection, managers may want to use two traps for detection of bark beetles, one baited with ethanol + α-pinene + ipsdienol and a second baited with ipsenol instead of ipsdienol. If the species of interest is I. avulsus, then managers may want to delete ethanol and α-pinene, as both compounds reduce catches of that species (Miller and Crowe 2018, Miller 2020). The best lure blend for I. avulsus is ipsenol + ipsdienol + lanierone (Miller et al. 2005).

With respect to predators, only the attraction of T. virescens to traps baited with ethanol + α-pinene was enhanced by the addition of either ipsdienol or ipsenol, with no benefit of including both compounds in the blend (Table 3). In contrast, catches of three other predatory species were enhanced by the addition of ipsenol but not ipsdienol. Addition of ipsdienol to traps baited with ipsenol negated the attractiveness of ipsenol in the blend for Lasconotus spp. (Table 3). Although ipsdienol enhanced catches of Platysoma spp., catches were highest in traps baited with ipsenol. Ipsdienol reduced catches of Platysoma spp. in traps baited with ipsenol (Table 3). For detection of predators, preference by managers for traps baited with ethanol + α-pinene + ipsenol may be in order. However, in management programs for bark and woodboring beetles, managers would likely prefer to avoid depletions of predators that may be controlling pest species. In such cases, ipsdienol should be the preferred compound to add to traps baited with ethanol + α-pinene.

In a study across North America, adding the binary blend of ipsdienol + ipsenol enhanced catches of Monochamus spp. in traps baited with ethanol + α-pinene (Miller et al. 2013). For two species of Cerambycidae in the present study, attraction to traps baited with ethanol + α-pinene was enhanced by the addition of ipsdienol or ipsenol, but there was no benefit of including both compounds in the blend (Table 3). There was no adverse effect of either compound on catches of four other species of cerambycids in traps baited with ethanol + α-pinene. Similar results were found with ipsdienol and ipsenol for Monochamus scutellatus (Say) and Monochamus clamator (LeConte) in traps cobaited with α-pinene or ethanol + α-pinene in British Columbia (Allison et al. 2003). However, it is possible that both ipsdienol and ipsenol may not be required for all these species. For example, ipsenol was as effective as monochamol (a pheromone used by numerous Monochamus spp.) in trapping four of seven species of Monochamus and enhanced catches in traps baited with monochamol for six of the seven species (Miller et al. 2016).

This study was conducted at one location in north-central Georgia. Clearly, additional studies are required with numerous other species over a broad geographic area. It is possible that the addition of other pheromones to traps baited with ethanol + α-pinene + ipsenol might yield better results than ipsdienol for a broad, generic lure blend for bark and woodboring beetles, at least in the Southeast. For example, various species of woodborers are attracted to traps baited with fuscumol and sulcatol in Georgia (Miller 2022). Allison et al. (2012b) found that catches of M. titillator and Monochamus carolinensis Olivier in traps baited with α-pinene were enhanced by the addition of the hardwood cerambycid pheromone syn-2,3-hexanediol. More focused research is required to develop multifunctional lure blends for the detection of bark and woodboring beetles in the future.