An apparatus for exposing insects to known concentrations of vapours from odorous liquids is described; it was used in a laboratory in England to test adult tsetse flies, Glossina palpalis (R.-D.) and G. morsitans Westw., obtained from Africa as pupae, and the blowfly, Phormia terraenovae R.-D. There is a definite pattern of behaviour of the flies in olfactory stimulants, in the final phase of which they are excited to fly. The number of seconds for which a fly is in flight gives a measure of its activation by the vapour. The method gives results comparable with those obtained with a standard choice-chamber technique and has considerable practical advantages for work with tsetse flies. The effects of concentrations of vapour, period of exposure, condition of the flies and external conditions on the response of tsetse flies to vapours were studied.

The response of G. morsitans and P. terraenovae to a selection of aliphatic acids, alcohols, esters and amines was determined, using a standardised procedure. There is a marked similarity between the two species in the concentrations of vapours required to activate them. The standard molar concentration, defined as the concentration of vapour required to raise the activity of the flies to a standard level of ten times that in pure air, was calculated for each compound tested from the regression of activity on concentration. Threshold concentrations (the highest concentrations that failed to raise fly-activity) were also calculated from the regression equations.