Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2003
Publication Date: February 25, 2004
Citation: Seitz, L.M., Ram, M.S. 2004. Metabolites of lesser grain borer in grains. Journal of Agricultural and Food Chemistry. 52:898-908. Interpretive Summary: Lessor grain borer (LGB, Rhyzopertha dominica) is an insect that causes major physical and off-odor damage to grain in storage. Technology for detecting and accessing the severity of infestation of this insect in grain during storage is needed. Two major aggregation pheromones of LGB, dominicalures 1 and 2, have been known for a number of years. In this research, we found that LGB also produces a wide array of minor ester compounds that are chemically related to the dominicalures. The minor metabolites were identified by using gas chromatography coupled with infrared and mass spectroscopy detectors to analyze the volatile compounds in cultures of LGB on wheat. Some of the metabolites were also observed in grain samples collected from grain storage and handing facilities, which showed that the compounds were produced in natural environments and not just in laboratory cultures. It appears that detection of the minor compounds in samples taken from grain storage facilities would indicate a high LGB population and/or presence of infestation for an extended time.
Technical Abstract: Many volatile alcohol and ester metabolites of lesser grain borer (LGB, Rhyzopertha dominica) cultured on wheat grain were identified. Volatiles from infested samples at 80 °C were collected on Tenax absorbent, thermally desorbed, and analyzed by gas chromatography (GC) using infrared (IR) and mass (MS) detectors for component identification. A solid-phase-micro-extraction (SPME) technique was used to analyze selected samples with a GC-MS system setup for obtaining chemical ionization mass spectra. SPME was also used in a synthesis process required to identify ester metabolites. Predominant compounds in LGB-infested grains were 2-pentanol and its esters of 2-methyl-2-pentenoic (A) and 2,4-dimethyl-2-pentenoic (B) acids which are known aggregation pheromones, dominicalures 1 and 2. 2-Pentanol esters of saturated A, beta-keto- and beta-hydroxy derivatives of A and B, homologues of A and B, and acid moieties lacking the 2-methyl substitution were found. Other straight- and branched-chain secondary alcohols and their esters were also observed . From reexamination of GC-MS-IR data acquired in our previous investigations of LGB cultured on sorghum grain and commercial samples in a grain odor study we showed the presence of many LGB metabolites in addition to the known dominicalures.