Multiple acceptors for pheromonal enantiomers on single olfactory cells in the Douglas-fir beetle,Dendroctonus pseudotsugae Hopk. (Coleoptera: Scolytidae).

Olfactory perception of pheromonal enantiomers by male and female Douglas-fir beetles,Dendroctonus pseudotsugae Hopk. (Coleoptera: Scolytidae), was investigated by electrophysiological techniques and behavioral bioassays. Electroantennograms (EAGs) and single-cell responses indicated both sexes to be more responsive to racemic frontalin and the (-)-enantiomer at lower dosages. At higher dosages, little difference was noted in responses to either enantiomer. However, response to the racemic mixture at higher dosages was slightly greater than responses to either enantiomer alone. In laboratory behavioral bioassays, responses to low concentrations of (-)-frontalin and the racemic mixture exceeded response to the (+)-enantiomer alone. At a higher concentration, responses to the racemic mixture or either enantiomer alone did not differ. The results indicate that separate enantiomer-specific acceptors may exist on the same pheromone receptor cell.

Single cell responses of the Douglas-fir beetle,Dendroctonus pseudotsugae hopkins (Coleoptera: Scolytidae), to pheromones and host odors.

Olfactory perception of pheromones and host odors byDendroctonus pseudotsugae males and females was investigated through single cell recordings. Responses of 71 cells (35 cells in males; 36 cells in females) were recorded to 1 µg of 10 pheromones and three host terpenes. The olfactory cells were classified into four types based on sensitivity and specificity for the various odors: (1) 3,2-MCHone (3-methyl-2-cyclohexenone) cells; (2) 3,2-MCHol (3-methyl-2-cyclohexenol) cells; (3) frontalin cells; and (4) synergist cells. 3,2-MCHone and 3,2-MCHol cells in both males and females were the most sensitive and specific of all cells recorded with a threshold ca. 0.001-0.01 µg on filter paper. Frontalin cells were less specialized than the two aforementioned cell types and had a somewhat higher threshold of ca. 0.01 µg. A larger percentage of these three cell types were recorded in males than in females. The synergist cells had the highest threshold of all recorded cell types and were the least specific. Each of these cells was most responsive to eithercis-verbenol,trans-verbenol, 1,2-MCHol, verbenone, α-pinene, or limonene; however, responses could be elicited by stimulation with other pheromones or host terpenes at higher dosages. Instances of inhibition of nerve impulse activity from spontaneously active cells were observed during 3,2-MCHol and 3,2-MCHone stimulation, thus suggesting multifunctional effects for these compounds. The results help explain the role of chemicals in host selection, aggregation, and colonization behavior of the beetle and further elucidate hypotheses put forth in an earlier electroantennogram study.

Antennal olfactory responsiveness of Douglas-fir beetle,Dendroctonus pseudotsugae Hopkins (Coleoptera: Scolytidae) to pheromones and host odors.

Electroantennograms were obtained fromD. pseudotsugae in response to the pheromones 3-methylcyclohex-2-en-1-one (3,2-MCHone), 3-methylcyclohex-2-en-1-ol (3,2-MCHol), frontalin,trans-verbenol, verbenone, and the host terpene hydrocarbons limonene and camphene. Male and female beetles were 10 and 100 times more sensitive to 3,2-MCH-one and 3,2-MCHol than to the other compounds. Of the other compounds, males were most sensitive totrans-verbenol, verbenone, and camphene, while females were most sensitive to frontalin, limonene, and camphene. The results parallel and help explain behavior of individual males and females during host tree selection, aggregation, and colonization.

Field bioassay ofexo- andendo-brevicomin withDendroctonus ponderosae in lodgepole pine.

Bothexo- andendo-brevicomin reduced the response of flyingDendroctonus ponderosae (Coleoptera: Scolytidae) to an attractant composed oftrans-verbenol and terpenes or oftrans- andcis-verbenol and terpenes in a stand ofPinus contorta var.murrayana. These data suggest that racemicexo- andendo-brevicomin may interrupt aggregation in populations of mountain pine beetle colonizing lodgepole pine; functions of the natural chiral compounds are unknown.

Sound production in scolytidae:chemostimulus of sonic signal by the douglas-fir beetle.

Stridulation by male Dendroctonus pseudotsugae was recorded in response to the natural female attractant (frass) or to three synthetic components of the attractant (frontalin, 3-methyl-2-cyclohexen-1-one, and trans-verbenol). This stridulation was acoustically distinct from stress sound and correlated with known attraction behavior. The response of female D. pseudotsugae to male stridulation-negation her attraction-was induced by playback of recorded attractant stridulation but not by that of stress sounds. Acoustic communication must be more important in scolytid behavior than it was heretofore believed to be.

Masking of the Aggregation Pheromone in Dendroctonus pseudotsugae Hopk.

The pheromone mask released by female Dendroctonus pseudotsugae Hopk. after the male stridulates stops aggregation of beetles in flight, but not arrestment of males, in an interaction of chemically and sonically induced behavior. This masking is viewed as a mechanism for survival through the regulation of attack and as a critical part of premating behavior.

Scolytid beetles associated with douglas fir: response to terpenes.

Douglas-fir oleoresin and the terpene hydrocarbons (alpha-pinene, beta-pinene, litnonene, camphene, geraniol, and alpha-terpineol) attracted various bark and timber beetles associated with Douiglas-fir forests during their flight. In responding to these volatile terpenes the bettles are directed to favorable breeding material.