T. L. Payne

Bark beetle olfaction. III. Antennal olfactory responsiveness ofDendroctonus frontalis Zimmerman andD. brevicomis Le Conte (Coleoptera: Scolytidae) to aggregation pheromones and host tree terpene hydrocarbons

Electroantennograms from males and females ofDendroctonus frontalis andD. brevicomis in response to serial dilutions of the pheromonesexo brevicomin and frontalin and the host terpene hydrocarbons 3-carene and α-pinene show no significant differences in the threshold concentration for response to the compounds for either sex or species. The intensity of response was greater to higher concentrations of the pheromones (10 to >104 μg) than the terpene hydrocarbons, suggesting the presence of more receptors on the antennae for pheromones than terpene hydrocarbons. Antennal olfactory responses to the compounds did not correlate to published data on behavioral responses by the beetles to the compounds in both field and laboratory studies. Adaptation experiments indicated that forD. frontalis, both frontalin andexo brevicomin share the same receptors on the antennae. The results indicated that the terpene hydrocarbons share some, but not all, of the same receptors.

Bark-beetle pheromones

The two major yeasts isolated from the southern pine beetle,Dendroctonus frontalis Zimmerman, areHansenula holstii Wickerham andPichia pinus (Hoist) Phaff; a third yeast,P. bovis van Uden et do Carmo-Sousa, has been isolated far less frequently. The main volatile metabolites produced by these yeasts are isoamyl alcohol, isoamyl acetate, 2-phenylethanol, and 2-phenylethyl acetate.We have found that certain of these compounds, particularly the esters, can greatly, enhance the attractiveness of a mixture of frontalin:trans-verbenol: turpentine (1:1:12), at certain limiting concentrations, to walking beetles in a laboratory bioassay.

Bombykal, a Sex Pheromone of the Sphinx Moth Manduca sexta

Abstract The first sex pheromone of a Sphinx moth has been isolated from Manduca sexta (Lepidoptera: Sphingidae) with the aid of an electroantennogram assay. It is attractive to males in a field test where its activity might be augmented by a second component in female extracts. Chemical tests and chromatographic properties identify the pheromone as a C16-aldehyde with a pair of conjugated double bonds. (E , Z)-0,12-hexadecadienal, (“bombykal”) was identical with the natural product. The comparison includes chromatography on three different capillary columns and determination of specific activities in the electroantennogram test.

Southern pine beetle: Olfactory receptor and behavior discrimination of enantiomers of the attractant pheromone frontalin

In laboratory and field bioassays, the response ofDendroctonus frontalis was significantly greater to the mixture of (1S, 5R)-(−)-frontalin andalpha-pinene than to (1R,5S)-(+)-frontalin andalpfa-pinene. Electro-physiological studies revealed that antennal olfactory receptor cells were significantly more responsive to (1S, 5R)-(−)-frontalin than to (1R, 5S)-(+)-frontalin. Both enantiomers stimulated the same olfactory cells which suggests that each cell possesses at least two types of enantiomer-specific acceptors.

Insect predator-prey coevolution via enantiomeric specificity in a kairomone-pheromone system.

Insect predators can be guided to their prey by a kairomonal response to the prey pheromone. We found this phenomenon to be highly specific in the bark beetle predatorThanasimus dubius. Olfactory responses and behavioral tests revealed that the predator is guided to its major preyDendroctonusfrontalis by the primary enantiomer of the pheromone of the prey, (1S, 5R)-(−)-frontalin. These and other findings suggest the co-evolution of a kairomone system of the predator and the pheromone system of its prey.

Structure and function of the sensilla on the antennal club of the southern pine beetle, Dendroctonus frontalis (Zimmerman) (Coleoptera: Scolytidae)

Abstract Four types of sensilla occur on the antennal club of Dendroctonus frontalis: fluted sensilla, sensilla trichodea II and III and sensilla basiconica. All but the sensilla trichodea III have cuticular pores. Electrophysiological studies show the sensilla trichodea II and basiconia to be olfactory sensitive hairs for beetle and host tree-produced volatiles. The sensilla trichodea III are mechanosensitive hairs. Electrophysiological data were not obtained for the fluted sensilla. The morphologies of the 4 sensillar types are described.

Bark beetle olfaction—II. Antennal morphology of sixteen species of Scolytidae (Coleoptera)

Abstract A SEM study was carried out on the antennae of several species of the scolytid genera Dendroctonus, Ips, Pseudohylesinus, Scolytus and Trypodendron . Although some genera have the same number of antennal segments, the shape of the antennal club was distinct for each genus. For all species the majority of sensilla occurred on the club and consisted of sensilla basiconica, sensilla chaetica and sensilla trichodea. The sensilla were arranged in sensory fields or bands on the club. Speculation is presented on the possible function of some of the sensilla.

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.

Chiral building units from carbohydrates-XIII. : Identification of the absolute configuration of endo-brevicomin from dendroctonus frontalis and synthesis of both enantiomers from d-ribose

Abstract The synthesis of both enantiomers of endo -7-ethyl-5-methyl-6,8-dioxabicyclo[3.2.l]octana ( endo -brevicomin, 12 and 12a ) starting froni D-ri-bose is described. Key interinediate is the open chain derivative 7 , a chiral building unit easily available from carbohydrates. Complexation gas chromatography showed the natural pheromone of males of the southern pine beetle, Dendroctonus frontalis Zimm. , to be (1R,5S,7S)- endo -brevicomin.

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.