Houseflies, Musca domestica, obtained from a high-larval-density culture were significantly (ca. 1.5 times) smaller than those from a low-larval-density culture. The same held true for their antennae and maxillary palps. Structure, number, and distribution of sensilla on antennae and palps of small and large flies were investigated using Scanning electron microscopy and Transmission electron microscopy. In each funiculus three pits were present, two (Type I) consisting of several compartments and one (Type II) of one compartment. Four types of olfactory sensilla were detected: trichoid sensilla on the funiculi, basiconic sensilla on funiculi and palps, grooved sensilla on funiculi and in pits Type I, and clavate sensilla on funiculi and in pits Type II. Type I pits also contained striated sensilla (presumably hygroreceptors). Mechanosensory bristles were present on scapes, pedicels, and palps. Noninnervated microtrichia were found on the palps and all antennal segments. The large houseflies possessed nearly twice as much sensilla as the small flies. So far, we did not observe differences in behavior between small and large flies. We assumed that small flies, being olfactory less equipped than large flies, may be able to compensate for this by, e.g., visual cues or by their olfactory sensilla being more sensitive than those of large flies. To be able to answer these questions careful studies have to be done on the behavioral responses of small and large flies to environmental stimuli. In addition, electrophysiological studies should be performed to reveal whether the responses of individual sensilla of flies reared under different conditions have been changed.

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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 effects of age on electroantennogram (EAG) responses were investigated in male and female Glossina morsitans morsitans and comparative studies on the effects of starvation and sex on the EAG in G.m. morsitans, G.austeni, G.tachinoides and G.fuscipes fuscipes were made. Stimuli were the vapours of l‐octen‐3‐ol, 4‐heptanone, 3‐nonanone and acetone. EAG decreased with age in both sexes of G.m.morsitans, responses in 5‐day‐old flies already being significantly lower than those in 1‐day‐old flies. In G.m.morsitans and G.tachinoides, EAG responses of males were higher than those of females. In G.austeni and G.f.fuscipes, however, the reverse was found. With increasing starvation EAG sensitivity increased in both sexes of G.m.morsitans and G.tachinoides. In G.austeni and in G.f.fuscipes no clear effects of starvation were observed. Response spectra of the individual species to the four odour substances did not change with increasing hunger. It is concluded that receptor sensitivity may be modulated depending on the insect's needs. Possible mechanisms of regulation and significance of this modulation are discussed.

A comparison was made of the EAG responses of repleted males and females of Glossina palpalis gambiensis Vanderplank, G. tachinoides Westwood, G. fuscipes fuscipes Newstead, G. morsitans morsitans Westwood and G. austeni Newstead to the odour of various concentrations of acetone, 4-heptanone, 3-nonanone and l-octen-3-ol. The stimulatory effectiveness of these substances increased in the order: acetone < 4-heptanone < 3-nonanone < l-octen-3-ol. Amounts of acetone 10M0 4 times greater and of 4-heptanone and 3-nonanone 10-100 times greater than those of l-octen-3-ol were required to obtain similar EAG responses. These results are discussed in relation to the behavioural effects of the odours of these substances on tsetse in wind tunnel experiments in the laboratory and catching experiments in the field. In G. m. morsitans and G. tachinoides, the EAG responses of males were somewhat higher than those of females. In G. austeni, G. f. fuscipes and G. palpalis gambiensis, however, the reverse occurred. All species were equally tuned to the four odour substances, which indicates that these odours do not determine host specificity. Resume-Une etude comparative des reponses electroantennographiques des males et des femelles deGlossina palpalis gambiensis Vanderplank, G. tachinoides Westwood, G. fuscipes fuscipes Newstead, G. morsitans morsitans Westwood et G. austeni Newstead a ete faite apres engorgement a diverses concentrations d'acetone, 4-heptanone, 3-nonanone et l-octen-3-ol. Les effets stimulants de ces substances augmentent dans l'ordre: acetone < 4-heptanone < 3-nonanone < l-octen-3-ol. Les quantites d'acetone 10 3 a 10 4 fois plus elevees et de 4-heptanone et 3-nonanone 10 a 100 fois plus elevees que celles de l-octen-3-ol etaient requises pour obtenir les reponses electroantennographiques semblables. Ces resultats sont mis en relation d'affaires avec l'impact des odeurs de ces substances sur le comportement des mouches tsetse dans le laboratoire et sur le terrain. Chez G. m. morsitans et G. tachinoides les reponses electroantennographiques des males etaient plus elevees que celles des femelles. Chez G. austeni, G. f. fuscipes et G. palpalis gambiensis les antennes des femelles etaient plus sensibles que celles des males. Toutes les especes etaient egalement sensibles aux 4 substances odorantes, ce qui indique que ces odeurs ne determinent pas de specificite d'hote.

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Abstract. The presence of background odour was found to have a small but significant effect on the sensitivity of the antennal olfactory system of houseflies, Musca domestica Linnaeus (Diptera: Muscidae), to new pulses of odour. We show that cross-adaptation and cross-sensitization between a background odour of (AE)-1-octen-3-ol and pulses of (AE)-1-octen-3-ol, 2-pentanone and R-( )-limonene can occur, confirming that olfactory receptor cells are sensitive to different odours. Background odour can increase the responses to low concentration odour pulses and decrease the responses to higher concentration odour pulses. It is suggested that background odour has a larger effect on olfactory receptor cells that respond with a tonic increase of spike frequency, giving information about the level of odour concentration, i.e. the`static' environment. Cells that respond in a phasic way only provide information on the dynamics of the olfactory environment.