Location: Commodity Protection and Quality
2012 Annual Report
Identification of the sex pheromone for NOW was completed recently. A four component sex pheromone blend was determined to be as attractive as females. Attractiveness of these four components was subsequently verified by a joint UC Riverside/ARS study. Preliminary field trials confirmed the 4-component blend could capture as many or more NOW males than females; however, lure effectiveness declined rapidly during the 4-day test.
This year we worked further on both gland extracts and volatile collections (below) to determine which steps in the analytical process led to skewed isomer ratios and/or skewed ratios between pheromone components. Gland extracts and pheromone volatiles were collected during the females’ optimal time of pheromone release. Glands were extracted in hexane and volatiles were collected from manually everted sex pheromone glands, with volatile collection on an open capillary. Collection of pheromone components on these open glass capillaries is particularly efficient since all the adhered odor molecules can be stripped from the capillary wall using just a few microliters of solvent. Five microliters of hexane forms a solid “slug” of solvent that moves through the capillary collecting the odor molecules; at the end of the capillary this solvent slug is removed with a gas chromatography (GC) syringe for immediate chemical analysis. As we have noted on numerous occasions, the conjugated dienes (three of the four pheromone components for NOW), are extraordinarily labile during collection and handling periods. Even movements of the plunger in an older syringe would lead to isomerization of these compounds. Therefore, all of our methods were re-analyzed, and practiced carefully until we obtained consistent results with synthetic and natural pheromone components. We have analyzed the release ratios of NOW pheromone molecules from cleaned rubber septa and found consistent ratios of three components. Release rates also were constant over a 29 day sample period.
We have developed handling methods for NOW pheromone release substrates and the volatiles collected from them that allow consistent release ratios and repeatable measurements of these volatiles.