The aims of this study were to investigate how antennal olfactory cells of tsetse (Diptera: Glossinidae) code odour quality and how they are able to discriminate between attractive and repellent odours. For Glossina pallidipes Austen, a survey is presented of the cells' responses to attractive (1-octen-3-ol, acetone, 3-methylphenol, carbon dioxide) and repellent stimuli (2-methoxyphenol, acetophenone, lactic acid, naphthalene). In addition, the responses of these cells to binary mixtures and the dose-response curves of 1-octen-3-ol, 3-methylphenol, 2-methoxyphenol and acetophenone are presented. A minority of the cells responded to one attractant or repellent only, whereas the vast majority were excited by more than one of the attractive and/or repellent stimuli. It is proposed that the peripheral olfactory cells of tsetse discriminate between different compounds via an across-fibre pattern coding, in which the cells that specifically code for attractants or repellents may play a substantial role in composing a unique excitation pattern that informs the central nervous system about the specificity of odours.

Using gas chromatography the relative amounts of (Z)‐9‐tricosene (muscalure) and some other hydrocarbons on the cuticle of 1‐ to 20‐day‐old houseflies (Musca domestica L.) from different strains were determined. Flies from a WHO strain, in culture since 1961, and first‐generation laboratory‐cultured flies from two wild‐type strains from a poultry breeding and a cow‐house with pigsty, respectively, were compared. On WHO females hydrocarbons with 23–25 C atoms constituted about 65% of the total hydrocarbons, whereas on wild‐type females less than 2% of these compounds was present. (Z)‐9‐tricosene comprised up to 20–30% of the total hydrocarbons on 5‐ to 20‐day‐old WHO females, whereas less than 0.5% (Z)‐9‐tricosene was present on the wild‐type females. We also compared the amounts of (Z)‐9‐tricosene and some other hydrocarbons on female houseflies, kept in culture in the laboratory for several generations. It appeared that whereas on first‐generation wild‐type females hardly or no (Z)‐9‐tricosene could be detected, the amounts of this substance had increased considerably after some tens of generations in the laboratory. It is suggested that this was due to selection in subsequent generations of high‐density populations. Production of (Z)‐9‐tricosene and of tricosane was shown to be closely linked. Selection did not affect the production of other cuticular hydrocarbons by the females. It is suggested that in mixed populations (both sexes together in a cage) in the course of time (Z)‐9‐tricosene is transferred from females to males and (Z)‐9‐heptacosene from males to females. It is concluded that reproductive ability of houseflies does not primarily depend on the amounts of (Z)‐9‐tricosene on females, although higher amounts of this substance may increase contacts between males and females.

The olfactory system of newly emerged houseflies (Musca domestica L.; Diptera, Muscidae) is already functional; very few differences compared to sexually mature houseflies exist for the responses to 1‐octen‐3‐ol, amylacetate, 2‐pentanone, 3‐methylphenol, R‐limonene, muscalure, and 6‐methyl‐5‐hepten‐3‐one. Sex differences are also almost absent, except for a higher sensitivity of females to acetic acid. Large differences exist between the sensitivity of antennae and palps to different odours. Antennae are sensitive to all odours tested. Palps are mainly sensitive to 3‐methylphenol and 2‐pentanone, both in percentage of responding cells and in response level. The sensitivity to amyl acetate was similar in palps and antennae. The responses to other odours were low in the palps. We conclude that traps baited with attractive odours may lure houseflies of all ages and both sexes.

In female mosquitoes of the anthropophilic species Anopheles gambiae Giles s.s. and the zoophilic An. quadriannulatus Theobald single sensillum recordings from grooved pegs were made. In both species, the majority of these sensilla responded to ammonium hydroxide, butylamine and propanoic acid, whereas a smaller part responded to acetone. Lactic acid, butanone, 3‐methyl phenol and 1‐octen‐3‐ol evoked responses in a minority of grooved pegs only. In An. gambiae these four substances evoked either excitatory or inhibitory responses. In An. quadriannulatus excitatory and inhibitory responses were only found on stimulation with lactic acid; butanone, 3‐methyl phenol and 1‐octen‐3‐ol only evoked inhibition in the pegs of this species. More than half of the grooved pegs responded to water vapour with an increase in spike frequency. As opposed to this, in some pegs inhibitory responses were found upon stimulation with vapour of low humidity. This suggests that grooved pegs may play a role in humidity perception in Anopheles. Dose‐response relations were investigated for cells excited by ammonium hydroxide, butylamine and propanoic acid. Excitatory responses to these three substances were dose‐dependent. No significant differences were found between the dose‐response curves of the two species. It is concluded that in both species the host odours tested are not perceived by specialist cells. Combined information from generalist cells may provide a detailed ‘odour profile’ of the host.