Richard J. Petroski

Male-produced aggregation pheromone ofCarpophilus obsoletus (Coleoptera: Nitidulidae).

Males ofCarpophilus obsoletus Erichson produce an aggregation pheromone to which both sexes respond. The pheromone was identified by GC-MS as (2E,4E,6E,8E)-3,5,7-trimethyl-2,4,6,8-undecatetraene (1), which is also a minor constituent of the pheromone blends ofC. hemipterus (L.),C. freemani Dobson, andC. lugubris Murray. The pheromone was synergized in wind-tunnel bioassays by propyl acetate, a “host-type” coattractant. In a dose-response study, 50 pg of1, plus propyl acetate, was significantly more attractive than just propyl acetate. Pheromone emission from groups of 65 males, feeding on artificial diet, averaged 2.2 ng/male/day. Emissions from individual males were larger, averaging 72 ng/day and ranging as high as 388 ng/day. Synthetic1 was tested in a date garden in southern California (500 µg/rubber septum), using fermenting whole-wheat bread dough as the coattractant. The pheromone plus dough attracted significantly more beetles than dough alone (means were 4.2 and 0.0 beetles per week per trap). Captured beetles were 54% females. Field trap catches were highest during the months of July and August.

Cuticular hydrocarbons and novel alkenediol diacetates from wheat stem sawfly (Cephus cinctus): Natural oxidation to pheromone components

The cuticular lipids of the wheat stem sawfly Cephus cinctus (Hymenoptera: Cephidae) were investigated as part of a chemical ecology project with this species. The major cuticular lipids were n-alkenes and n-alkanes. Alkenes were the most abundant and exhibited dramatic sexual dimorphism. (Z)-9-Tricosene accounted for about half of the total hydrocarbon in males but was nearly absent from females. The dominant alkenes in females were (Z)-9-pentacosene and (Z)-9-heptacosene. The alkane profiles were similar in both sexes, with n-tricosane being the most abundant, followed by n-pentacosane and n-heptacosane. In both sexes, there were minor amounts of alkanes and alkenes with other chain lengths and n-alkadienes of 29 and 31 carbons. In males, about one tenth of the surface lipids consisted of (Z)-9-alkene-1, ω-diol diacetates with 22-, 24-, and 26-carbon chains. The same compounds were also detected from females but in much smaller amounts. The structures of these novel diacetates were proven by synthesis. By analogy to methyl oleate, a well-studied food lipid, the alkenes and diacetates were expected to undergo slow oxidation in air to release specific aldehydes and other volatile products, and these were generally detected in volatiles collected from living sawflies. Atmospheric oxidation of the diacetates was also demonstrated in the absence of sawflies. One product from the diacetates, 9-acetyloxynonanal, was shown in other research to be particularly active electrophysiologically and was also attractive in the field. Aldehydes from the alkenes also showed strong electrophysiological activity. The concept of volatile pheromones originating from heavy, unsaturated cuticular lipids is discussed.

Identification of a Female-Specific, Antennally Active Volatile Compound of the Currant Stem Girdler

We identified (Z)-9-octadecen-4-olide as a female-specific, antennally active compound from the currant stem girdler Janus integer Norton. Female specificity was demonstrated by gas chromatographic comparison of liquid chromatography fractions of male and female volatile emissions and whole body extracts. The γ-lactone was identified by coupled gas chromatographic-electroantennographic detection (GC-EAD), coupled gas chromatographic-mass spectrometric (GC-MS) analysis, microchemical reactions, and GC and MS comparison with authentic standards. GC-EAD analysis of female volatile emissions and cuticular extracts showed a single peak of activity on male antennae, which was not present in male-derived materials. Female antennae did not respond to any of the tested materials. The hydrogenation product of the natural EAD-active material was a known saturated γ-lactone. The mass spectrum of the dimethyl disulfide derivative of the natural γ-lactone was consistent with a double bond present in the 9 position. Comparison of the natural γ-lactone and a synthesized racemic mixture of (Z)-9-octadecen-4-olide on a chiral GC column showed the presence of a single enantiomer in the natural material.

Biosynthesis of (2E,4E,6E)-5-ethyl-3-methyl-2,4,6-nonatriene: the aggregation pheromone of Carpophilus freemani (Coleoptera: Nitidulidae)☆

Abstract The biosynthesis of the male-produced aggregation pheromone of Carpophilus freemani Dobson (Coleoptera: Nitidulidae) was studied by feeding the beetles on diet containing organic acids labeled with 2 H (acetate, propionate, and butyrate) or 13 C (acetate). The emitted pheromone, (2 E ,4 E ,6 E )-5-ethyl-3-methyl-2,4,6-nonatriene, was collected and analyzed by mass spectrometry and NMR spectrometry to determine the positions of isotopic labels. Studies with four deuterium-labeled synthetic pheromone standards demonstrated that mass spectrometry would be useful in locating the labels in beetle-derived samples. The pheromone is built up from one acetate unit, one propionate unit, and then two butyrate units, accompanied by the loss of the carboxyl carbon from one of the butyrates. The beetles will use propionic and butyric acid if it is available in the diet, but they are capable of making these acyl units from acetate if necessary. Biosynthetic steps for removing the acyl oxygens and making the double bonds of the pheromone are proposed to be as in usual fatty acid anabolism (reductions and dehydrations).

The Loline Group of Pyrrolizidine Alkaloids

Pyrrolizidine alkaloids are of common occurrence in plants, particularly in genera such as Senecio, Crotalaria, Symphytum, Echium and Heliotropium (1). Retronecine (1) and heliotridine (2), and numerous simple and complex esters of these and related alkaloids, are typical pyrrolizidines. Many pyrrolizidine alkaloids are potent hepatotoxins and carcinogens (2); thus, the pyrrolizidines have been widely studied and are considered to be among the most important groups of natural products in terms of their effects on human health and economic activities (3).

Male-produced aggregation pheromone compounds from the eggplant flea beetle (Epitrix fuscula): identification, synthesis, and field biossays.

Volatiles from the eggplant flea beetle, Epitrix fuscula Crotch (Coleoptera: Chrysomelidae), feeding on host foliage, were investigated. Six male-specific compounds were detected and were identified through the use of mass spectrometry, nuclear magnetic resonance (NMR) spectrometry, chiral and achiral gas chromatography, high-performance liquid chromatography, electrophysiology (gas chromatography-electroantennography, GC–EAD), and microchemical tests. The two most abundant of the six compounds were (2E,4E,6Z)-2,4,6-nonatrienal (1) and (2E,4E,6E)-2,4,6-nonatrienal (2). The other four compounds, present in minor amounts, were identified as himachalene sesquiterpenes; two of these, 3 and 4, were hydrocarbons and two, 5 and 6, were alcohols. All four sesquiterpenes were previously encountered from male flea beetles of Aphthona spp. and Phyllotreta cruciferae. Synthetic 1 and 2 matched the natural products by GC retention times, mass spectra, and NMR spectra. Sesquiterpenes 3–6 similarly matched synthetic standards and natural samples from the previously studied species in all ways, including chirality. Both natural and synthetic 1 and 2 gave positive GC–EAD responses, as did sesquiterpenes 3, 5, and 6. Field trials were conducted with a mixture of 1 and 2, and the baited traps were significantly more attractive than control traps to both male and female E. fuscula. The E. fuscula pheromone has potential for monitoring or controlling these pests in eggplants.

IMPROVED HORNER-WADSWORTH-EMMONS PREPARATION OF α-METHYL- OR α-ETHYL-α,β-UNSATURATED ESTERS FROM ALDEHYDES

The E-isomer selectivity of the Horner-Wadsworth-Emmons olefination of aldehydes to form α-methyl- or α-ethyl-α,β-unsaturated esters has been improved by using lithium tert-butoxide as the base, triethyl-2-phosphonopropionate or triethyl-2-phospho-nobutyrate as the phosphonate, an aldehyde, and hexane as the reaction solvent. Greater E-isomer selectivity was observed in the formation of α-methyl-α,β-unsaturated esters than α-ethyl-α,β-unsaturated esters. These compounds are useful intermediates for the synthesis of insect pheromones and natural products.

Field Capture of Northern and Western Corn Rootworm Beetles Relative to Attractant Structure and Volatility

We used field assays to study attraction of feral northern and western corn rootworm beetles (Diabrotica barberi and D. virgifera virgifera) to a series of mostly nitrogenous and benzenoid synthetic compounds allied with host plant and floral aromas. Vaporization rates were obtained for most field-tested compounds and selected additional lures under both ideal and field-representative, but constant, conditions. Although many test compounds showed at least trace activity for one or both species, methyl benzoate and some of its derivatives, notably methyl anthranilate and methyl 4-methoxybenzoate, merited emphasis as effective new lures for females. Structural alteration of methyl benzoate had consistently negative effects on northern corn rootworm captures despite variable effects on release rate, whereas western corn rootworm was more strongly attracted to methyl anthranilate and methyl 4-methoxybenzoate than to the considerably more volatile parent compound. Phenylacetaldoxime was attractive to females of both species, but no more so than syn-benzaldoxime, included as reference. Release rate was disproportionately low for benzaldoxime, as well as other nitrogenous lures, under field compared with ideal conditions. The attractiveness of salicylaldoxime to northern corn rootworm, despite its low field release rate, and the unattractiveness of methyl salicylate, having a methyl ester in place of the oxime group, similarly highlighted importance of the oxime moiety for reactivity of this species.

Bioactivity, Synthesis, and Chirality of the Sex Pheromone of Currant Stem Girdler, Janus integer

It was previously reported that females of the currant stem girdler, Janus integer Norton (Hymenoptera: Cephidae), produce a compound, (Z)-9-octadecen-4-olide (1), that is sensitively detected by the antennae of males only. These characteristics suggested a pheromonal function, and this has now been confirmed with behavioral tests. Field tests conducted during two seasons in a commercial red currant field in Washington State showed that synthetic racemic 1 is attractive to male J. integer under natural conditions. A clear dose-response was evident, with greatest numbers of girdlers caught in sticky traps baited with 10 mg of the pheromone (in rubber septa) and least in traps baited with 1 mg or less. During May 2002, 10, 5, 3, and 1 mg baited traps caught means of 41.4, 26.6, 6.7, and 2.7 males/trap/visit (3–5 day intervals), respectively, with a maximum of 229 males caught in a single trap baited with 5 mg. A new synthetic method for racemic 1 is presented. The absolute configuration of natural 1 from the male sawflies was determined to be (R). The potential for using the sex pheromone of J. integer to improve management of this currant and gooseberry pest is discussed.

Preparation and Deprotection of Aldehyde Dimethylhydrazones

Abstract Aldehydes were conveniently protected as dimethylhydrazones by stirring a mixture of the aldehyde, N,N‐dimethylhydrazine, anhydrous magnesium sulfate, and dichloromethane at room temperature. Azeotropic removal of water, formed during the course of the reaction, was not required because anhydrous magnesium sulfate functions as a water scavenger. Deprotection of aldehyde dimethylhydrazones was accomplished by stirring a mixture of the aldehyde dimethylhydrazone and aqueous glyoxylic acid at room temperature. The reaction time for the preparation and deprotection of aldehyde dimethylhydrazones varied with the structure of the aldehyde. The mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.