Abstract
Three cryptic species in the Euwallacea fornicatus species complex were reared in laboratory colonies and investigated for the presence of pheromones. Collections of volatiles from combinations of diet, fungus, beetles, and galleries from polyphagous shot hole borer (Euwallacea sp. #1) revealed the presence of 2-heneicosanone and 2-tricosanone only in the presence of beetles, regardless of sex. Subsequent examination of volatiles from the other two species, tea shot hole borer (Euwallacea sp. #2) and Kuroshio shot hole borer (Euwallacea sp. #5), revealed these two ketones were present in all three species but in different ratios. In dual choice olfactometer behavioral bioassays, mature mated females were strongly attracted to a synthetic binary blend of ketones matching their own natural ratios. However, females in each species were repelled by ketone blends in ratios corresponding to the other two species. Males of each species responded similarly to females when presented with ratios matching their own or the other two species. The presence of these compounds in the three beetle species, in ratios unique to each species, and their strong species-specific attraction and repellency, suggests they are pheromones. The ecological function of these pheromones is discussed. In addition to the pheromones, the previously known attractant (1S,4R)-p-menth-2-en-1-ol (also known as quercivorol) was discovered in the presence of the fungal symbionts, but not in association with the beetles. Quercivorol was tested in a dual-choice olfactometer and was strongly attractive to all three species. This evidence suggests quercivorol functions as a kairomone for members of the E. fornicatus species complex, likely produced by the symbiotic fungi.
Highlights
Until several decades ago, ambrosia beetles were not considered economically or ecologically important pests of living trees because the vast majority of them cultivate their ambrosiaHow to cite this article Cooperband et al (2017), Pheromones of three ambrosia beetles in the Euwallacea fornicatus species complex: ratios and preferences
Independent studies have concluded that populations of beetles morphologically identified as E. fornicatus, that stem from four separate invasions in the United States (Hawaii, Florida, and two in southern California), are composed of three genetically distinct, cryptic species of ambrosia beetles in what is recognized as the E. fornicatus species complex (Eskalen & Stouthamer, 2012; Eskalen et al, 2013; O’Donnell et al, 2015; Stouthamer et al, 2017)
All three species morphologically resemble E. fornicatus, but they are genetically different enough to be considered different species, and carry different species of fungal symbionts in the genus Fusarium (O’Donnell et al, 2015; Carrillo et al, 2016). They have yet to receive unique scientific names, but they are commonly referred to as: the polyphagous shot hole borer (PSHB) (Euwallacea sp. #1), which was first detected in Los Angeles County, CA in 2003 (Eskalen et al, 2012; Eskalen et al, 2013); the tea shot hole borer sensu lato (TSHB) (Euwallacea sp. #2), which was first detected in Hawaii in 1910 (Schedl, 1941) and more recently in Miami-Dade County, FL in 2002 (Rabaglia et al, 2008); and the Kuroshio shot hole borer (KSHB) (Euwallacea sp. #5), which was first detected in San Diego County, CA in November 2013 (Eskalen et al, 2013; O’Donnell et al, 2015; Carrillo et al, 2016; Boland, 2016; Stouthamer et al, 2017; Dodge et al, 2017)
Summary
Ambrosia beetles were not considered economically or ecologically important pests of living trees because the vast majority of them cultivate their ambrosiaHow to cite this article Cooperband et al (2017), Pheromones of three ambrosia beetles in the Euwallacea fornicatus species complex: ratios and preferences. With the sharp increase of global trade in recent years, we have seen an increase of invasive ambrosia beetles capable of causing major economic and ecological damage, and severely threatening native forest ecosystems (Marini et al, 2011) Such is the case with members of the Euwallacea fornicatus species complex (Coleoptera: Curculionidae: Scolytinae). All three species morphologically resemble E. fornicatus, but they are genetically different enough to be considered different species, and carry different species of fungal symbionts in the genus Fusarium (O’Donnell et al, 2015; Carrillo et al, 2016) They have yet to receive unique scientific names, but they are commonly referred to as: the polyphagous shot hole borer (PSHB) Avocado is threatened in California and Florida, and more than one quarter of all street trees in southern California are reproductive hosts susceptible to attack (Lesser, 1996; Eskalen & Stouthamer, 2012; Mendel et al, 2012; Freeman et al, 2013b; Eskalen et al, 2013; Carrillo et al, 2016; Cooperband et al, 2016; Kendra et al, 2017; Stouthamer et al, 2017)
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