Evidence that (+)-endo-Brevicomin is a Male-Produced Component of the Southern Pine Beetle Aggregation Pheromone

Abstract

Previous research indicated that the aggregation pheromone of the southern pine beetle, Dendroctonus frontalis, is produced only by females, the sex that initiates attacks. We provide evidence indicating that secondarily arriving males augment mass aggregation by releasing the attractive synergist (+)-endo-brevicomin. Healthy pines artificially infested with both sexes of D. frontalis were significantly more attractive to conspecifics than trees infested solely with females. Coupled gas chromatography-electroantennographic detection (GC-EAD) analyses of volatiles isolated from male beetles revealed substantially greater olfactory sensitivity by D, frontalis to endo-brevicomin than to any other component. The threshold of detection of both sexes for (+)-endo-brevicomin was four orders of magnitude lower than for its antipode and at least one order of magnitude lower than for either enantiomer of frontalin, the major female-produced aggregation pheromone component. Pairing with a female in a gallery stimulated individual male beetles to produce hundreds of nanograms of (+)-endo-brevicomin. (4-)-endo-Brevicomin was detected in a small percentage of female D. frontalis, whereas (-)-endo-brevicomin was never detected in either sex. In field trapping bioassays, we confirmed that (+)-endo-brevicomin is a potent synergist for attractive combinations of frontalin and pine turpentine. However, (+)-endobrevicomin failed to attract D. frontalis either when presented alone or in combination with turpentine. We postulate that mass colonization of host trees by D. frontalis is mediated by distinct semiochemicals from both sexes rather than females alone. Our discovery of a key aggregation pheromone component in such an apparently well-studied species implies that the pheromone models of other bark beetles could benefit from systematic reexamination using newer technologies. Additionally, baits fortified with (+)-endo-brevicomin may enhance pest management strategies that exploit attractants for D. frontalis.

Spatial Displacement of Release Point can Enhance Activity of an Attractant Pheromone Synergist of a Bark Beetle

“…All three traps were baited with frontalin and turpentine, and the release rate of (+)-endo-brevicomin from the 0 m trap was varied. min, and host monoterpenes; Sullivan et al 2007), only (+)-endo-brevicomin and frontalin appeared to mediate beetle discrimination among closely-spaced traps (experiment 4, Table 3). Beetle captures were concentrated in traps that were relatively closer to a frontalin source, but relatively more distant from a (+)-endo-brevicomin source (Table 3).…”

“…The capillaries and autosampler vial inserts were secured in the vial with a silicone GC septum that was pressed sideways into the vial mouth; the sealed end of each capillary (or the tapered tip of each insert) was inserted into a pinhole in the interior-facing edge of the septum. (+)-endo-Brevicomin was synthesized as described elsewhere (Sullivan et al 2007) and was >99% enantiomerically and 95% chemically pure by GC (contaminants with no known behavioral activity). Racemic endo-brevicomin [PheroTech (now ConTech Inc.), Delta, BC, Canada] was 95% chemically pure (<1% exo-brevicomin contamination).…”

“…Infestations typically occur across the landscape in spatially discrete, rapidly expanding "spots" in which adjacent trees are attacked in succession by beetles arriving from the surrounding forest as well as by re-emerging parent and brood adults from within the infestation (Gara 1967;Gara and Coster 1968). Aggregation is mediated by a complex of semiochemicals: initially-attacking females release the attractive pheromone component frontalin, which is enhanced synergistically both by monoterpene kairomones (particularly α-pinene) released by the host pine and (+)-endo-brevicomin from secondarily-arriving males (Smith et al 1993;Sullivan et al 2007). Additionally, the female-produced pheromone component transverbenol may substitute for host monoterpenes when the latter are at low levels, and may play an important role in initiating host colonization (Renwick and Vité 1969;Payne et al 1978a).…”

“…Studies performed with racemic endo-brevicomin indicated that this compound acts as an attractant antagonist (Vité and Renwick 1971;Payne et al 1978a;Salom et al 1992). In contrast, baits composed of pure (+)-endo-brevicomin (only enantiomer produced by the species) strongly enhanced attraction to combinations of frontalin and host odors (Vité et al 1985;Sullivan et al 2007), and led these authors to conclude that this compound was a component of the D. frontalis aggregation pheromone. (+)-endo-Brevicomin alone does not attract D. frontalis into traps (Sullivan et al 2007).…”

Southern Pine Beetle, Dendroctonus frontalis, Antennal and Behavioral Responses to Nonhost Leaf and Bark Volatiles

“…Odors associated with the host and, in particular, the volatile fraction of pine resin (i.e., pine turpentine) appear to be important to this semiochemical blend. Pine turpentine components are released in high concentrations from beetle attack sites together with beetle pheromones (Pureswaran and Sullivan, 2012), and can enhance responses to the beetle's attractive pheromone components by one to two orders of magnitude (Billings, 1985;Sullivan et al, 2007b;authors' unpublished data). α-Pinene, the predominant constituent of turpentine of the major host species of D. frontalis within the southeastern United States, is the main active component of the host's odor blend (Renwick and Vité, 1969).…”