Choice test olfactometers

Choice tests for trail pheromones are similar in concept to the bioassays using Y-tube or multiple-arm olfactometers, and eventually the subject is confronted with a choice between two or more substances. Choices are recorded, and the frequency of choices is analyzed by G-test against the null hypothesis of choices of equal frequency. 

The method of statistical analysis in many bioassays focuses on analyzing the number and pattern of choices made by subjects. In general, these assays will not involve truly continuous variables, but will involve counts, e.g., the number of times that each branch of an olfactometer was chosen, the number of times that upwind flight was observed, the number of eggs deposited on test or control substrates, or the number of times that test or control feeding substrates were selected. Such data often are distributed following a Poisson distribution and can... 

If flight is essential for behavioral choices to be made, then there may be no alternative to the wind tunnel. These are larger and more expensive than olfactometers, and few allow the diversity of choices provided by multiarm olfactometers. Nevertheless, a number of variables can be measured in wind tunnels relating to the time and intensity of various behavior responses of test organisms to odor (e.g.. Baker Carde 1984) (Table 5.1). 

In one series of tests, animals were given a choice of air pulled from a communal cage that housed other frogs or an empty aquarium. These sources were hidden from the view of the test animals. In another series of experiments, animals were housed in aquariums for three weeks with potting soil, sphagnum moss, a water dish, a plastic hide box and two plants (Rheo discolor) and a bromeliad (Neoregelia). Animals were placed in the olfactometer and tested to see if they could discriminate between (1) home and empty aquarium odors, (2) home versus potted Coleus plant odors, (3) bromeliad versus Coleus odors, or (4) home versus bromeliad odors. 

Y-tube olfactometers (Figure 6.4) are generally used to measure the level of attraction or repulsion of host-seeking mosquitoes to volatile stimuli in choice experiments. " Clean and conditioned air constantly runs through the tube system to the end of the base leg, where mosquitoes are connected. During stimulus application, mosquitoes are allowed to fly upwind into a decision chamber to choose between a test cage that holds the test stimulus and a control cage with clean air. 

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