A versatile and quantitative volatile-delivery system for laboratory bioassays

A versatile moving-air system is described for delivering volatiles into a wind tunnel or other bioassay device. The system controls up to four volatile sources at one time. There is a calibrated, adjustable splitter for each source so that any percentage of a source's airstream, or none of it, can be directed to the system outlet at any moment. Thus, the system allows the sample volatiles to be bioassayed in any order and at any level or in mixtures of any desired proportions. Volatile sources of many types can be used, including single chemicals in slow-release formulations, mixtures of chemicals, or volatiles from living organisms. The volatile stream can be sampled by solid-phase microextraction (SPME) just before it enters the wind tunnel. Analysis of the SPME sample by gas chromatography allows absolute delivery rates of volatile components to be calculated. System performance was characterized with physical measurements and with bioassay experiments involving Carpophilus humeralis (F.) (Coleoptera: Nitidulidae). One bioassay experiment demonstrated how volatiles from a microbial culture (fermenting bread dough) and a synthetic counterpart (an aqueous solution of acetaldehyde, ethanol, I-propanol, isobutanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and ethyl acetate) could be compared at a range of dose levels, with just one sample of each type. These natural and synthetic volatile sources delivered very similar amounts of the above compounds and produced nearly identical dose-response curves. In another experiment, three bread dough volatiles (ethanol, acetaldehyde, and ethyl acetate) were tested in mixtures. Each component was used at four different levels (giving a total of 64 experimental treatments), but just one physical sample was needed for each chemical. The experiment provided clear information about response thresholds and interactions among these host volatiles. The volatile delivery system is versatile, easy to operate, and can be constructed from inexpensive materials.