Tympanal hearing organs are widely used by insects to detect sound pressure. Such ears are relatively uncommon in the order Diptera, having only been reported in two families thus far. This study describes the general anatomical organization and experimentally examines the mechanical resonant properties of an unusual membranous structure situated on the ventral prothorax of the tsetse fly, Glossina morsitans (Diptera: Glossinidae). Anatomically, the prosternal membrane is backed by an air filled chamber and attaches to a pair of sensory chordotonal organs. Mechanically, the membrane shows a broad resonance around 5.3–7.2 kHz. Unlike previously reported dipteran tympana, a directional response to sound was not found in G. morsitans. Collectively, the morphology, the resonant properties and acoustic sensitivity of the tsetse prothorax are consistent with those of the tympanal hearing organs in Ormia sp. and Emblemasoma sp. (Tachinidae and Sarcophagidae). The production of sound by several species of tsetse flies has been repeatedly documented. Yet, clear behavioural evidence for acoustic behaviour is sparse and inconclusive. Together with sound production, the presence of an ear-like structure raises the enticing possibility of auditory communication in tsetse flies and renews interest in the sensory biology of these medically important insects.

Tsetse flies Glossina pallidipes Austen and G. morsitans morsitans Westwood deposit their larvae in warthog burrows, in August–November, at Rekomitjie Research Station, Zambezi Valley, Zimbabwe. Artificial burrows, made from 200–l steel drums, were used to sample these flies and to collect their puparia. Sand-filled plastic trays in the burrows served as a substrate for larval deposition. The sand was covered with c. 2 cm of leaf litter after it was shown that only 3% of larvae were deposited on bare sand if both substrates were available. Other burrow modifications – artificially shading the burrow entrance, increasing the relative humidity inside the burrow, or reducing the size of the burrow entrance – significantly decreased deposition rates. The use of burrows in the hot season results in a reduction in the temperature experienced by the puparium towards an assumed optimum level of 26°C. Artificial burrows maintained a mean temperature of 28.5°C during October-November 1998, c. 2.5°C cooler than ambient; earlier work has shown that natural burrows can be c. 5°C cooler than ambient at these times. This may explain why natural burrows in full sunlight were used for larviposition, whereas artificial burrows were used only when they were in deep shade, and why significantly higher proportions of G. pallidipes were found in natural (66%) than in artificial burrows (34%). Better-insulated artificial burrows might produce more puparia with higher proportions of G. pallidipes. Burrows become waterlogged during the rains and may be too cool for optimum puparial development during the rest of the year. The percentages of G. m. morsitans in catches of females from artificial burrows, refuges and odour-baited traps were 34, 26 and < 10% respectively. Traps are biased in favour of G. pallidipes; artificial burrows may show a bias in favour of G. m. morsitans that is a function of temperature. Artificial warthog burrows provide a convenient way of studying the puparial stage in tsetse and for the first time facilitate the capture of females as they deposit their larvae.

The haemolymph of the tsetse, Glossina morsitans morsitans, contains a low molecular weight protein of very high density (1.29 g/mi). The protein was detected in the haemolymph during all developmental stages of the insect. Purification of the protein was achieved by a combination of density gradient ultracentrifugation and repeated gel permeation chromatography. Electrophoresis under non-denaturing and denaturing conditions showed the protein to be a single polypeptide chain (M,˜23,000). Amino acid analysis revealed a relatively high content of the acidic amino acids as well as serine and glycine. The protein contained lipids as shown by Sudan Black staining but was nonglycosylated. Using rabbit antiserum against the isolated protein in immunodiffusion and immunoblotting experiments, no cross-reactivity was detected with haemolymph samples from insects representing six orders. Although the function of the protein remains unknown, its uniqueness to Glossina suggests that it may have a role in the physiology of this insect.

Behavioural and electrophysiological (EAG) studies were undertaken to determine the olfactory selectivity of the antennae of Glossina morsitans morsitans Westwood and Glossina pallidipes Austen to phenolic kairomones. Responses of both species to 3-alkylphenols increased as the alkyl chain increased from one carbon atom to three, while the opposite trend was observed with 4-alkylphenols. These results indicated that 4-cresol and 3-n-propylphenol are the most stimulatory of the two respective groups of phenols. However, comparison of the responses indicated differences in the sensitivities of the chemoreceptor systems of the two species. Hence different compositions of the phenols may be required to best attract these species. Probable interactions of the phenols with the binding sites on the receptor surface are discussed.

Responses of tsetse Glossina morsitans morsitans and Glossina pallidipes (Diptera: Glossinidae) to host-derived phenolic kairomones were investigated using a wind tunnel. Activation behaviour of G. m. morsitans depended on the mixture of the phenols but not on the dose or ratio of the blend used. Up wind orientation behaviour and actual contact with the odour source depended on both the phenolic mixture and on the ratio of the phenols in the blend. In the present studies, a 4:1 blend of 4-cresol and 3-n-propylphenol, respectively, consistently induced more of the flies to fly upwind and contact the odour source as compared to any other combination of the phenols or even when these two crucial phenols were mixed in a ratio of 9:1; the ratio in which they are found in a typical sample of buffalo urine.

Comparison of the responses of the two species indicate that significantly fewer G. m. morsitans fly upwind and contact the odour source on stimulation with a blend of 4-cresol and 3-n-propylphenol as compared to G. pallidipes. This may explain why phenols only produce small improvements in the catches of G. m. morsitans as compared to G. pallidipes.

The simple wind tunnel developed, not only provides a useful tool for rapidly screening candidate attractants, but also a means to investigate how various compounds alone or in various combinations affect tsetse behaviour.

Chlordimeform (CDM), tested by topical application, was found to be toxic to both male and female tsetse with the maximum effect some 72 hr after treatment. Median lethal doses were approx. 0.4 μg/fly for unfed adult tsetse of both sexes, 100% mortality at 72 hr was achieved with 2 μg/fly. Mature fed females were less susceptible to chlordimeform, the median lethal dose for 72 hr being 12.5 μg/fly. High doses of chlordimeform depressed the weight of puparia from survivors, but had no effect upon fecundity. Sublethal doses caused a significant depression of feeding activity, but did not cause hyperactivity or disrupt fat body lipid reserves.

The anterior aorta is rich in axons and axonal endings originating from the nervus corporis cardiacum (NCC) and the corpus cardiacum (CC). Neurosecretory granules in the NCC axons are small compared to large granules synthesized in the CC. Vesiculation of the secretory granules into clusters of small vesicles occur both in NCC axonal endings and axon-like processes from the CC, suggesting that both types of secretions are released into the haemolymph.

Synapses occur between the NCC axons and cardiac muscle cells, as well as with cell processes from the CC, suggesting that some of the neurohormes from the NCC axons may function as neurotransmitters. The CC consists of large neuron-like cells, that synthesize an intrinsic secretion; it also contains a neuropil of NCC axons and CC cell processes. There is no evidence of a separate storage and release lobe in the CC. No synapses occur between the axons and cell processes or with the cell bodies. The CC cell processes have their endings in the aortic wall where they make synapses with NCC axonal endings and where they most likely release their material. It is suggested that in Glossina: (a) the aortic wall has taken over the neurohaemal role of the CC whose function otherwise remains that of synthesizing an intrinsic hormone; and that (b) the activity of the CC to synthesize and/or release its intrinsic secretion is most likely controlled in the aortic wall via a neurotransmitter substance.

The suitability of the East African goat and various types of hybrid goats to serve as hosts for tsetse was compared over an extended period. Although there was no significant difference between indigenous and hybrid goats when feeding up to 350 flies per host, about 94% more indigenous goats than hybrid goats became unsuitable as hosts and required a prolonged period of rest when the fly burden was increased to 450 flies per host. Of the hybrid types assessed, Toggenburg crosses were best suited as hosts even though they required more frequent rest periods than the other hybrid types.

Polyacrylamide gel disc electrophoresis of the salivary secretion from the tsetse, Glossina morsitans morsitans Westwood, showed 11 protein bands, four of which were characterized as glycoproteins. Sixteen amino acids and four sugars in the hydrolysates of saliva were identified. Thin layer chromatography showed five lipid classes and three phospholipids. The secretion is a clear, transparent, viscous fluid with a pH between 7.00 and 7.5. These findings are discussed in relation to the nutritional requirements of the metacyclic forms of trypanosomes that may be found in the salivary glands.