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ARS Home » Pacific West Area » Parlier, California » San Joaquin Valley Agricultural Sciences Center » Commodity Protection and Quality Research » Research » Publications at this Location » Publication #307578

Title: Measure your septa release ratios: pheromone release ratio variability affected by rubber septa and solvent

item Kuenen, Lodewyk
item Siegel, Joel

Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2014
Publication Date: 3/31/2015
Citation: Kuenen, L.P., Siegel, J.P. 2015. Measure your septa release ratios: pheromone release ratio variability affected by rubber septa and solvent. Journal of Chemical Ecology. 41:303-310.

Interpretive Summary: Pheromone lures are commonly made by applying pheromone components, dissolved in an organic solvent, to a rubber septum/sleeve stopper (used in serum bottles). Although there have been numerous studies of the release rate decay from these septa, they have been conducted with indirect and time consuming methods that obscure the variability of the release ratios of the compounds applied to the septa. Here we show that there is a high variability in release ratios of pheromone components due in part to the solvent in which the pheromone was applied. In addition, these release ratios decrease logarithmically over time (three weeks in this study), yet the variability remains. This high variability, though documented here, is likely not predictable; therefore we formally urge researchers to use these new rapid and easy analysis methods to assess their test septa prior to use in bioassays so that future studies may be better compared and contrasted.

Technical Abstract: The type of solvent and volume of the solvent used to load pheromone/volatile components onto rubber septa had significant effects on release ratios, the variability of those release ratios, and the recoverability of the volatile components during subsequent extraction with hexane. Volatile release ratios of Oriental fruit moth (OFM) pheromone and additional volatile compounds were determined using a GC column as a volatile trap for rapid collection, elution, and analysis from individual rubber septa (ca. one hr. total). Volatile compound solutions were prepared in hexane, pentane, CH2Cl2, and MTBE and 10, 30, and 100 µl aliquots of each solution were applied to rubber septa. Septa loaded with 100 µl of CH2Cl2 emitted significantly higher OH:Ac ratios than septa loaded with the other solvents, which were all similar. Four compounds of near-equal mass: 1-dodecanol, 1-dodecenal, methyl decanoate, and tridecane emitted different release ratios dependent on the solvent, hexane or CH2Cl2, with which the septa were loaded. The more polar the compound the slower it was emitted from the septa regardless of solvent. Similarly, these solvents affected the release ratios of three aliphatic alcohols. Release ratios of the alcohol and acetate components of the OFM pheromone components were assessed over a three-week period with septa loaded with each solvent. Regardless of loading solvent, the OFM OH:Ac ratios declined logarithmically over the three weeks; however, the decay slope from septa loaded with CH2Cl2 solutions was significantly different from those of the other three solvents, which were nearly all the same. Overall a high variability in the OH:Ac release ratios was measured regardless of the solvent used or the volume it was applied in. These results suggest that researchers should assess the release ratios from septa to be used in bioassays rather than just reporting the type of septum, ratios of compounds applied, and solvent used to prepare them.