Oxidation Products of Pinene the Bark Beetle, Dendroctonus Frontalis

by Dr. Molly Darr | Jun 16, 2022 | 1971-1980 Publications

Abstract

Southern pine beetles were collected as they emerged from infested pine bolts and exposed in Petri dishes to α- and β-pinene for 20 hr. Changes in the volatile contents of the beetles’ hindguts were detected by gas chromatography, and previously unidentified components were characterized by mass, i.r., and n.m.r. spectroscopy. A prominent compound in hindguts of both sexes before and after treatment was identified as myrtenal, and a less conspicuous, male-specific compound proved to be myrtenal. Upon exposure to α-pinene, males produced cis– and trans-verbenol, 4-methyl-2-pentanol was found in both sexes. Compounds present after treatment with β-pinene vapour were identified as trans-pinocarveol in both sexes, and pinocarvone in the males.

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Spatial Distribution of Mite Associates of Within-tree Populations of Dendroctonus frontalis Zimm.

by Dr. Molly Darr | Jun 16, 2022 | 1971-1980 Publications

Abstract

Bark beetles exposed to vapours of terpene hydrocarbons produce alcohols and ketones, apparently by oxidation at allylic positions. The predictability of such oxidations has now been extended to include non-terpenoid hydrocarbons. Exposure of Dendroctonus frontalis to 1-methyl l-cyclohexene resulted in the production of seudenol (3-methyl-2-cyclohexen-l-ol), a pheromone of D. pseudotsugae, along with the corresponding ketone and other alcohols. The most abundant of these was identified as 1-cyclohexenemethanol. A rearrangement product of seudenol, also believed to be present in D. pseudotsugae hindguts, was identified as 1-methyl-2-cyclohexen-l-ol. A similar rearrangement was detected upon exposure of D. frontalis females to ~-pinene. In addition to cis– and trans-verbenol, cis-3-pinen-2-ol was found in the hindguts. A general mechanism of oxidation and rearrangement is suggested, as further exemplified by the production of trans-pinocarveol and myrtenol by beetles exposed to β-pinene.

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OXIDATION OF UNSATURATED CYCLIC HYDROCARBONS BY DENDROCTONUS FRONTALIS

by Dr. Molly Darr | Jun 16, 2022 | 1971-1980 Publications

Abstract

Bark beetles exposed to vapours of terpene hydrocarbons produce alcohols and ketones, apparently by oxidation at allylic positions. The predictability of such oxidations has now been extended to include non-terpenoid hydrocarbons. Exposure of Dendroctonus frontalis to 1-methyl l-cyclohexene resulted in the production of seudenol (3-methyl-2-cyclohexen-l-ol), a pheromone of D. pseudotsugae, along with the corresponding ketone and other alcohols. The most abundant of these was identified as 1-cyclohexenemethanol. A rearrangement product of seudenol, also believed to be present in D. pseudotsugae hindguts, was identified as 1-methyl-2-cyclohexen-l-ol. A similar rearrangement was detected upon exposure of D. frontalis females to ~-pinene. In addition to cis– and trans-verbenol, cis-3-pinen-2-ol was found in the hindguts. A general mechanism of oxidation and rearrangement is suggested, as further exemplified by the production of trans-pinocarveol and myrtenol by beetles exposed to β-pinene.

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Sampling Intensity, Informational Content of Samples, and Precision in Estimating Within-Tree Populations of Dendroctonus frontalis

by Dr. Molly Darr | Jun 16, 2022 | 1971-1980 Publications

Abstract

The practice of quantitatively sampling within-tree populations of Dendroctonus frontalis was investigated by comparing the relationships between sampling intensity, informational content of samples, and precision in estimation. Random and stratified random sampling plans were compared and contrasted to selective or purposeful sampling using the tree geometry model-probability density function (TG-PDF) estimation procedure. The random techniques required large quantities of data and were therefore less suitable than the TG-PDF procedure. The latter procedure incorporates knowledge of the vertical distribution of the D. frontalis life stages and therefore required much less data for a given level of precision. The TG-PDF procedure was evaluated on the basis of precision obtained in using the technique on different numbers of sample levels and the position of the sample levels. Precision as judged by the refined standard deviation of the estimate αR increased as the number of levels sampled increased. For a given number of levels, the refined αR, which associates covariables with the sample levels, always produced a better estimate than the basic standard deviation αB which assumed equal information from each sample level. Positioning of sample levels along the infested bole influenced the precision obtained. Dispersing the sample levels over the infested bole while avoiding the extremes generally resulted in better precision for each life stage. The precision in estimation was best where the informational content C of the individual levels was similar.

The optimal location for sample levels varied with the life stage being sampled. Generally 2 or 3 levels provided an adequate estimate for most sampling requirements. The emerging adult life stage was the most variable and therefore the more difficult and costly to sample.

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Field Response of the Southern Pine Beetle to Behavioral Chemicals

by Dr. Molly Darr | Jun 16, 2022 | 1971-1980 Publications

Abstract

Field tests were conducted in East Texas in 1973-77 to evaluate the influence of 7 behavioral chemicals on the flight and landing behavior of the southern pine beetle, Dendroctonus frontalis Zimmerman. A mixture of frontalin plus host tree volatiles attracted flying beetles within an infestation. Trans-verbenol synergized the activity of frontalin and substituted for host tree volatiles, α-pinene and loblolly turpentine. Verbenone in a 1: 1 ratio with frontalin did not significantly affect trap catch. At higher concentrations of verbenone, trap catch was significantly reduced. Endo-brevicomin inhibited trap catch when added to an attractant-baited trap. Exo-brevicomin showed no inhibitory effect. Traps with a 1:4 mixture of endo-brevicomin and verbenone plus an attractant caught significantly fewer beetles than traps with the attractant plus either one of the inhibitors.

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