Lloyd E. Browne

Brevicomin: Principal Sex Attractant in the Frass of the Female Western Pine Beetle

The principal component of the sex attractant produced by the female western pine beetle (Dendrotonus brevicomis) is exo-7-ethyl-5-methyl-6,8-dioxabicyclo[3.2.1]octane; the trivial name brevicomin is suggested.

Pheromonal attraction and allomonal interruption ofIps pini in California by the two enantiomers of ipsdienol

Air containing volatile compounds from around maleIps pini boring in ponderosa pine logs from California was condensed, fractionated by GC, and assayed in the laboratory and field. The only fraction that showed consistent activity in laboratory assays contained a single compound identified as ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol). Synthetic racemic ipsdienol showed no activity in either the laboratory or field. However, (−)-ipsdienol, the naturally occurring enantiomer, was attractive toI. pini in the laboratory and field, whereas (+)-ipsdienol interrupted the response ofI. pini to a natural source of attraction in field tests. (−)-Ipsdienol is a major component of the attractant pheromone of this species, since its level of activity in laboratory assays was quantitatively comparable to that of the condensed volatiles, and it was as attractive as maleI. pini boring in ponderosa pine in the field. (+)-Ipsdienol is a component of the pheromone of the competing species,I. paraconfusus.

Sex pheromones of bark beetles—I. Mass production, bio-assay, source, and isolation of the sex pheromone of Ips confusus (LeC.)☆

Abstract Methods for mass producing pheromone-laden male frass in kg quantities are described. Individual male productivity is 9·4 mg/day and lasts for about 15 days. Three kg were utilized in the described isolation work. Experiments established decisively the presence of the pheromone on and throughout the dense faecal pellet. The attractant was found to be present in frass produced by males boring in white fir and Douglas fir, indicating that the sex pheromone does not function in initial host discrimination. A previously described bio-assay which utilizes simultaneously released groups of female or male beetles was refined. Their movement to the source of the attractant and their klinotactic behaviour in the olfactometer established the basis of the bio-assay. A detectable response is evoked by dilutions of benzene extracts equivalent to 3 × 10−8 g of frass, which is about that produced by one male in one-third of a second. Isolation is initiated by soaking and pulverizing the frass several times in warm benzene. Benzene was removed by distillation and the concentrate distilled over a short path under reduced pressure. The distillate was chromatographed on silica gel by gradient elution with an ethyl ether-benzene mixture. Two internal markers bracketing the active silica gel fraction were identified as nonanal and geranyl acetate. The active fraction was subjected to gas-liquid chromatography, using a column of silicone rubber SE 30 on Chromosorb G, and good recovery of active material was achieved representing only 0·0007 per cent of the weight of starting material. Further GLC fractionation was performed on Carbowax 20M with the activity occurring as a number of partially resolved minor peaks.

Identification of two new terpene alcohols from frass produced by Ips confusus in ponderosa pine

Abstract Two new terpene alcohols have been isolated from frass produced by Ips confusus feeding in ponderosa pine. They are (−)-2-methyl-6-methylene-7-octen-4-ol and trans-2-methyl-6-methylene-3,7-octadien-2-ol as determined by spectral analyses; they serve as internal markers in the isolation of the sex pheromone.

Relationship between a host plant compound, myrcene and pheromone production in the bark beetle, Ips paraconfusus.

Abstract The pheromonal components, ipsenol and ipsdienol were found in increasing quantities in hindguts of only the male sex of Ips paraconfusus following exposure of both sexes to a series of increasing concentrations of myrcene vapour. Hindguts of female and male beetles contained similar quantities of myrcene and other volatile compounds associated with myrcene exposure. Unexposed beetles of both sexes did not contain detectable amounts of any volatile compound. This indicates that myrcene induces or is a precursor for sex-specific pheromone biosynthesis.

Novel trapping and delivery systems for airborne insect pheromones

Abstract A cryogenic air liquefaction technique was developed for totally recovering volatile insect pheromones. Compounds thus trapped are metered and released into the air during field assays with power-driven micro-syringes and during laboratory assays by evaporation from the lower end of disposable micro-pipettes.

Quantitative estimates of the western pine beetle attractive pheromone components,exo-brevicomin, frontalin, and myrcene in nature

Three parameters are described for estimating the natural occurrence of chemically defined insect pheromones: (1) the rate and duration of release by the insect, (2) the density of the pheromone-emitting insect population in both time and space, and (3) dispersal and degradation rates of the chemicals. Each of these parameters, except dispersal, was estimated for a population ofDendroctonus brevicomis LeC, and its three component attractive pheromones. A single generation of 610,000 beetles, believed to comprise the entire population in a 65-km2 forest, was estimated to have released 0.78, 3.7, and 370.5 g of frontalin,exo-brevicomin, and myrcene, respectively, within a 30-day period.

Identification of linalool produced by two species of bark beetles of the genus Ips

Abstract The terpene alcohol linalool (3,7-dimethyl-1,6-octadien-3-ol) has been isolated from volatiles produced by Ips paraconfusus females and from frass produced by I. pini males, both insects boring in ponderosa pine. Neither species of either sex responds to linalool in the laboratory bioassay. Pitfalls involved in identification of some terpene alcohols are noted.

A trapping system for the western pine beetle using attractive pheromones

A trapping system utilizing attractive pheromones is described for the suppression and survey of western pine beetle,Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae), populations over large forested areas and for extended periods of time. Two types of compactable sticky traps are described. A large vane trap was developed for population suppression. It consists of 6 m2 of trapping surface comprised of four sticky coated fabric panels supported with a telescoping mast. A smaller cylindrical shaped trap with 0.19 m2 trapping surface was developed for survey purposes. Perchloroethylene cleaning devices were developed to remove insects from both traps. Methods for sample splitting and sequential counting of the sub-samples were developed to estimate numbers of insects on the suppression traps. Experiments were conducted to evaluate the efficacy of both the traps and the counting procedures.

Feeding and boring behavior of the bark beetle,Ips paraconfusus, in extracts of ponderosa pine phloem

MaleIps paraconfusus Lanier bored and fed in cellulose powder substrates treated with solvent extracts of ponderosa pine phloem in preference to cellulose powder alone. Stimuli that elicit boring and feeding behavior occurred in the water extracts and the combined solvent extracts. No significant boring or feeding occurred in the methanol extract. There was a preference for, but no significant feeding in, the water partition of the ether extract. Feeding, but no preferential boring, occurred in the ether extracts.