Quantitative Assessment of Insect Olfactometer Performance by Experimental Flow Analysis

Biocontrol organisms respond to olfactory cues with behavior which can affect their efficacy as pest control agents. Investigations into olfactory stimuli and responses often use four-armed olfactometers for laboratory experiments. Performance evaluations of the olfactometers have generally been qualitative and based on visual assessment. A quantitative technique for characterizing the air flow and gas mixing in a four-armed olfactometer was developed. Ethylene gas was injected into the flow stream for each channel of the olfactometer. Samples of air at various locations in the olfactometer chamber were drawn through hypodermic probes and the concentration of ethylene in the samples were determined by gas chromatography. Flow boundaries between adjacent channels were not distinct and mixing between channels was observed, although concentration spatial gradients were high in the boundary regions. Mixing increased as flow neared a central outlet. Gross assessments of organism behavior in olfactometers appear valid in spite of flow mixing.