Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2001
Publication Date: N/A
Interpretive Summary: Knowledge of how pest insects use chemical scents to find others of their kind or their host plants has led to new ways of managing the pests in an environmentally friendly manner, such as using pheromone traps to monitor pest populations and to decide when (or whether) to apply pesticides. Research to gain such knowledge has recently begun for the wheat stem sawfly, a perennial pest of wheat in the northern Great Plains. Another study at NCAUR has identified chemicals that the sawflies emit to attract mates (pheromones). The present report demonstrates that key pheromone components can originate simply from the weathering (oxidation) of oils on the sawfly body surface. Some of these oils are novel compounds that have not been previously encountered in nature. The oxidation of surface oils into pheromone components is a very unusual mechanism for natural pheromone production, and this sawfly may provide a useful model species for future research on this topic.
Technical Abstract: 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-penatcosane and n-heptacosane. In males, about one tenth of the surface lipids consisted of (Z)-9-alkene- 1,omega-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 detected in volatile collections from living 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.