Abstract
Research over the last 15 years has revealed widespread parsimony of a number of highly conserved pheromone motifs within the Cerambycidae (Insecta: Coleoptera). These conserved pheromones have been exploited to develop synthetic volatile pheromone lures, which has led to the emergence of pheromone-baited trapping as a valuable tool to capture and study cerambycids. We used pheromone-baited traps in 2014 to 2016, including traps baited with conserved pheromone motifs, to collect field data in western Idaho to address existing knowledge gaps in pheromone-based interactions and community ecology of cerambycids in the Pacific Northwest and Intermountain Region of the United States. Our overall objective was to utilize pheromone-baited trapping to examine the species composition, richness, diversity, evenness and community dynamics within and among cerambycid assemblages at sites in western Idaho and to examine the possible role of volatile pheromones in these parameters. Our trapping bioassays captured two species, Centrodera dayi Leech (Lepturinae: Rhagiini) and Phymatodes (Phymatodes) vulneratus (LeConte) (Cerambycinae: Callidiini) that represented new state records for Idaho. Analysis of headspace volatiles collected from captured beetles demonstrated (R)-2-methylbutan-1-ol to be a male-produced volatile pheromone for Phymatodes dimidiatus (Kirby). Our trapping results indicated that flight periods overlapped for P. dimidiatus, Phymatodes hirtellus (LeConte), Phymatodes nitidus LeConte and P. (P.) vulneratus (LeConte) (Cerambycinae: Callidiini) for sites and years combined, while flight periods of the sympatric species P. dimidiatus, P. hirtellus and P. nitidus also overlapped at the same site and year. Given this overlap in flight periods, these species may be utilizing other biological and/or behavioral mechanisms to ensure reproductive isolation.
Our trapping results suggested a regional split between populations of Tragosoma harrisii LeConte and T. soror Laplante (Prioninae: Meroscelisini) within Idaho, with T. harrisii captured in higher numbers in the northern portion and T. soror captured in higher numbers in the southern portion of the region sampled. The flight periods of T. harrisii and T. soror overlapped at all site-year replicates where both species were captured, suggesting that flight period phenology was not being used as a mechanism to maintain reproductive isolation between these species. A likely mechanism is the utilization of opposite enantiomers of the (2,3)-hexanediol pheromone structure.
Additional analyses testing attraction among 13 synthetic volatile pheromone lures found a significant treatment effect for nine cerambycid species. Likely attractants for two of the species were racemic 3-hydroxyoctan-2-one for Clytus planifrons (LeConte) (Cerambycinae: Clytini), and racemic 2-methylbutan-1-ol for Xylocrius agassizi (LeConte) (Cerambycinae: Callidiini).
The results for our cerambycid community analysis comparing the Shannon diversity index (H’), species richness (S’) and the Shannon evenness (J’) index found that all three measures differed among site-years, while the analyses for species richness, diversity and evenness of cerambycid captures among pheromone treatments across all site-years showed a significant difference among treatments only for species evenness. We describe a method to develop a region-specific, multi-component pheromone lure that maximizes the capture of total cerambycid species, which can also target individual species of interest. Such a method could produce a cost-effective lure to monitor cerambycid communities and potential invasive and/or rare or endangered species in western Idaho and other regions.