EAG recordings were made from both males and females of Cydia fagiglandana (Zell.) and C. splendana (Hb.) on stimulation with the tortricid sex attractants (E,E)‐8,10‐dodecadien‐l‐yl acetate (E8E10‐12:Ac), (E,E)‐8,10‐dodecadien‐l‐ol (E8E10‐12:OH) and (Z)‐8‐dodecen‐l‐yl acetate (Z8‐12:Ac). The dose‐response curves of the various attractants were almost identical for males of both species. The order of increasing EAG sensitivity was E8E10‐12:OH < Z8‐12:Ac < E8E10‐12:Ac. In females, EAGs increased in the order E8E10‐12OH < E8E10‐12:Ac < Z8‐12:Ac. They were much less sensitive to the sex attractants; the EAG amplitudes to E8E10‐12:Ac were 20–50 times smaller than those of males. The antennae of C. fagiglandana females were about twice more responsive to the sex attractants than those of females of C. splendana. Recordings from single antennal olfactory cells of C. fagiglandana males showed responses of 1 or 2 cells on stimulation with the sex attractants and with volatiles from chestnut leaves. The diel spontaneous locomotor activities of both species as measured in actographs ran almost concurrently. Most moths were active during the first 4–6 h and the last 2.5 h of the night. During the day the moths were inactive, except females of C. splendana which already showed some activity at the end of the afternoon. A correlation appeared to exist between the locomotor activities and behavioural responsiveness to attractive odours. Behavioural responses of males and females were studied in a wind‐tube in the presence and the absence of an airstream. Female calling behaviour was observed. Results suggested that E8E10‐12:Ac is a main component of the female sex pheromone of both Cydia species. A stream of air, whether or not loaded with attractants, always induced antennal elevation and grooming of the antennae and palps in both males and females. Responses to upwind attractants only occurred after switching off the airstream. It is proposed that either (1) attractive odours in combination with an airstream may evoke an ‘internal excitatory state’ that finds active expression in standing air or that (2) intermittent stimulation with odours, which may occur in the unsteady air shortly after switching off the airflow, is indispensable for inducing upwind displacement. Branches of chestnut attracted both sexes and functioned as arrestants. Contrary to what was found in several other moth species, signals from the host plant did not appear to induce pheromone production. Males as well as females were attracted to E8E10‐12:Ac, to calling conspecific females and to the smear of abdomen tips cut off from calling conspecific females. With a paper loaded with E8E10‐12:Ac and three conspecific females present in the tube, the females lined up about 20 cm from each other and started to call. These results suggested that sensitivity of the females to their own sex attractants may permit them to detect the presence of other calling females, leading to settling and synchronization of pheromone production, and avoidance of pher...

The present study was initiated to gain insight into the way in which tsetse flies (Glossina spp.) sense odours at different locations in odour plumes in both an open field and a wooded area. We recorded the antennal responses (EAGs) from stationary living female G. pallidipes 15 m upwind and at various (60, 40, 20, 10, 5 and 1 m) distances downwind from a synthetic host odour source (containing 1‐octen‐3‐ol, acetone and two phenols), in the natural habitat of the fly (Zimbabwe) using a portable electrophysiological device. Experiments were performed in a flat open area (an airstrip) and in riverine woodland. Differences between responses in different environments were determined by comparing various parameters of the EAGs (intermittency, frequency, amplitude, duration and rate of depolarization). We found that a fly senses odours as puffs that, further downwind, contain less odour and pass less frequently. In an open field downwind from the source, tsetse perceive more olfactory information than upwind for only 10–20 m, whereas in woodland, olfactory responses remain higher and more frequent than upwind up to at least 60 m. In an open field, olfactory information rapidly increases when approaching the odour source from 20 m and in woodland from 5 m onwards. It is proposed that averaging odour information over time may be of minor importance in long‐range location of odour sources. The results suggest that tsetse may smell odour‐baited targets from at least 60 m downwind and that the number of flies responding to and being caught by these baits may be higher in woodland than in an open field.

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.

Spike trains from individual antennal olfactory cells of tsetse flies (Glossina spp.) obtained during steady-state conditions (spontaneous as well as during stimulation with 1-octen-3-ol) and dynamic stimulation with repetitive pulses of 1-octen-3-ol were investigated by studying the spike frequency and the temporal structure of the trains. In general, stimulation changes the intensity of the spike activity but leaves the underlying stochastic structure unaffected. This structure turns out to be a renewal process. The only independently varying parameter in this process is the mean interspike interval length, suggesting that olfactory cells of tsetse flies may transmit information via a frequency coding. In spike records with high firing rates, however, the stationary records had significant negative first-order serial correlation coefficients and were non-renewal. Some cells in this study were capable of precisely encoding the onset of the odour pulses at frequencies up to at least 3 Hz. Cells with a rapid return to pre-stimulus activity at the end of stimulation responded more adequately to pulsed stimuli than cells with a long increased spike frequency. While short-firing cells process information via a frequency code, long-firing cells responded with two distinctive phases: a phasic, non-renewal response and a tonic, renewal response which may function as a memory of previous stimulations.