Polytene chromosome maps in four species of tsetse flies Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans (Diptera: Glossinidae): a comparative analysis

Photographic polytene chromosome maps from pupal trichogen cells of four tsetse species, Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans were constructed and compared. The homology of chromosomal elements between the species was achieved by comparing banding patterns. The telomeric and subtelomeric chromosome regions were found to be identical in all species. The pericentromeric regions were found to be similar in the X chromosome and the left arm of L1 chromosome (L1L) but different in L2 chromosome and the right arm of L1 chromosome (L1R). The L2 chromosome differs by a pericentric inversion that is fixed in the three species, G. pallidipes, G. morsitans morsitans and G. m. submorsitans. Moreover, the two morsitans subspecies appeared to be homosequential and differ only by two paracentric inversions on XL and L2L arm. Although a degree of similarity was observed across the homologous chromosomes in the four species, the relative position of specific chromosome regions was different due to chromosome inversions established during their phylogeny. However, there are regions that show no apparent homology between the species, an observation that may be attributed to the considerable intra—chromosomal rearrangements that have occurred following the species divergence. The results of this comparative analysis support the current phylogenetic relationships of the genus Glossina.     

Changing visual responsiveness in pregnant and larvipositing tsetse flies, Glossina morsitans

ABSTRACT. Direct observations on the spontaneous activity and visually-evoked responses of pregnant female Glossina morsitans morsitans Westw. were made hourly during the photophase over the 4 days around larviposition. Visual stimulation was by a 5-wide vertical black stripe moving laterally, 4 times min^-1 at c. 5 s^-1. The numbers of take-offs and the numbers of females taking off were recorded, both in response to the stimulus and spontaneously in its absence. The visual responsiveness paralled both the day-to-day changes and the altered circadian patterns of spontaneous activity reported previously (Brady & Gibson, 1983), being very low for the 48 h before parturition. It did not, however, rise in parallel with the increase in spontaneous activity during the last 3–4 h before parturition, and the proportion of flights oriented towards the moving stripe was also much reduced at that time. The significance of this changing responsiveness to slow movement is discussed, and its potential enhancement of any behavioural avoidance of aerosol, non-residual insecticide spraying during late pregnancy is noted.     

Copulatory behaviour of the tsetse flies Glossina morsitans and G.austeni

ABSTRACT. The copulatory behaviour of Glossina morsitans morsitans West. and G.austeni Newst. was analysed by filming. After a male and female engaged genitalia, the male performed a repertoire of five actions for 3–4 min: (1) 'rubbing' his metathoracic, tibiotarsal joint against the region of genital contact; (2) 'stroking' or hitting the female's head and thorax with his meso- and metathoracic legs; (3) 'wing flick' by moving his mesothoracic legs in a rowing motion whilst at the same time vibrating the wings as in normal flight; (4) 'wing vibration' with the wings vibrated in the closed position; (5) 'wings out' in which the wings are moved out to the flying position without any observable vibration. Each action was repeated many times, to give variable individual sequences, but declined in frequency exponentially over the first 3–4 min in copulo. The two species differed in the frequency of acts. Shortly before separation, a few hours later, actions 1 and 2 reappeared. Receptive females exhibited little overt behaviour except in the maintenance of a passive stance. Refractory females rejected a mating attempt by flexing the abdomen ventrally, vibrating their wings in the closed position, and pushing the male with meso- and metathoracic legs. The significance and possible functions of male behaviour are discussed in relation to mating in Glossina and other Diptera.     

Two Tsetse fly species, Glossina palpalis gambiensis and Glossina morsitans morsitans, carry genetically distinct populations of the secondary symbiont Sodalis glossinidius

Genetic diversity among Sodalis glossinidius populations was investigated using amplified fragment length polymorphism markers. Strains collected from Glossina palpalis gambiensis and Glossina morsitans morsitans flies group into separate clusters, being differentially structured. This differential structuring may reflect different host-related selection pressures and may be related to the different vector competences of Glossina spp.     

Circadian activity patterns in three species of tsetse fly: Glossina palpalis, austeni and morsitans

ABSTRACT. Observations on the nature and control of spontaneous flight activity in tsetse flies have so far been made only on G. m. morsitans Westw. This paper reports preliminary observations of the same kind on two other species: G. p. palpalis (R.-D.) and G. austeni Newst. The flight pattern of all three species consisted of short bursts of activity (usually lasting <1 min) separated by long intervals of rest, changes in activity level occurring exclusively as changes in the frequency of these flight bursts. In constant conditions in LD 12:12, G. palpalis and G. austeni were almost totally diurnal, with strongly predominant afternoon activity peaks, but a slight tendency to decrease activity around noon as occurs to a much greater extent in G. morsitans. This rhythm persisted in constant darkness (DD), but whereas in most G. morsitans only the morning peak was retained in DD, in G. palpalis and G. austeni it was only the afternoon peak. The loss of the afternoon peak in G. morsitans may be due to the very low activity levels in DD. Food deprivation led to increased activity in all three species, most markedly so in G. palpalis and G. austeni , in which the amount of activity per day increased c. ten-fold over three days' post-emergence starvation.     

Geographical distribution of Glossina palpalis gambiensis and G.p.palpalis in Liberia

The two subspecies of Glossina palpalis (Robineau-Desvoidy) occurring in Liberia could be reliably separated morphometrically by measuring the width of the terminal dilatations of the male inferior claspers. Subspecies differentiation of female flies was less conclusive. Identification of flies from fifty-four sites revealed that most of Liberia lies in the belt of Glossina palpalis palpalis. However, pure and substantial populations of G.p.gambiensis Vanderplank occur north of 8 degrees 20'N in the north-west of Liberia.     

Variations in attack behaviours between Glossina palpalis gambiensis and G. tachinoides in a gallery forest suggest host specificity

Tsetse flies Glossina palpalis gambiensis and G. tachinoides are among the major vectors of sleeping sickness (Human African Trypanosomiasis‐HAT) and nagana (African Animal Trypanosomiasis – AAT) in West Africa. Both riparian species occur sympatrically in gallery forests of south west Burkina Faso, but little is known of their interspecies relationships although different authors think there may be some competition between them. The aim of this study was to check if sympatric species have different strategies when approaching a host. A man placed in a sticky cube (1 m × 1 m × 1 m) and a sticky black‐blue‐black target (1 m × 1 m) were used to capture tsetse along the Comoe river banks in a Latin Square design. The number and the height at which tsetse were caught by each capture method were recorded according to species and sex. Glossina p. gambiensis was more attracted to human bait than to the target, but both species were captured at a significantly higher height on the target compared with the human bait (P < 0.05). No significant difference in heights was found between G. tachinoides and G. p. gambiensis captured on targets (33 and 35 cm, respectively, P > 0.05). However, catches on human bait showed a significant difference in height between G. tachinoides and G. p. gambiensis (22.5 and 30.6 cm, respectively, P < 0.001). This study showed that these sympatric species had different attack behaviours to humans, which is not the case with the target. The implications of these findings are discussed.     

Sodalis glossinidius (Enterobacteriaceae) and Vectorial Competence of Glossina palpalis gambiensis and Glossina morsitans morsitans for Trypanosoma congolense Savannah Type

Sodalis glossinidius is an endosymbiont of Glossina palpalis gambiensis and Glossina morsitans morsitans, the vectors of Trypanosoma congolense. The presence of the symbiont was investigated by PCR in Trypanosoma congolense savannah type-infected and noninfected midguts of both fly species, and into the probosces of flies displaying either mature or immature infection, to investigate possible correlation with the vectorial competence of tsetse flies. Sodalis glossinidius was detected in all midguts, infected or not, from both Glossina species. It was also detected in probosces from Glossina palpalis gambiensis flies displaying mature or immature infection, but never in probosces from Glossina morsitans morsitans. These results suggest that, a) there might be no direct correlation between the presence of Sodalis glossinidius and the vectorial competence of Glossina, and b) the symbiont is probably not involved in Trypanosoma congolense savannah type maturation. It could however participate in the establishment process of the parasite.     

Responses of tsetse flies, Glossina morsitans morsitans and Glossina pallidipes, to baits of various size

Recent studies of Palpalis group tsetse [Glossina fuscipes fuscipes (Diptera: Glossinidae) in Kenya] suggest that small (0.25 × 0.25 m) insecticide-treated targets will be more cost-effective than the larger (≥1.0 × 1.0 m) designs currently used to control tsetse. Studies were undertaken in Zimbabwe to assess whether small targets are also more cost-effective for the Morsitans group tsetse, Glossina morsitans morsitans and Glossina pallidipes. Numbers of tsetse contacting targets of 0.25 × 0.25 m or 1.0 × 1.0 m, respectively, were estimated using arrangements of electrocuting grids which killed or stunned tsetse as they contacted the target. Catches of G. pallidipes and G. m. morsitans at small (0.25 × 0.25 m) targets were, respectively, ～1% and ～6% of catches at large (1.0 × 1.0 m) targets. Hence, the tsetse killed per unit area of target was greater for the larger than the smaller target, suggesting that small targets are not cost-effective for use against Morsitans group species. The results suggest that there is a fundamental difference in the host-orientated behaviour of Morsitans and Palpalis group tsetse and that the former are more responsive to host odours, whereas the latter seem highly responsive to visual stimuli.     

Two Tsetse Fly Species, Glossina palpalis gambiensis and Glossina morsitans morsitans, Carry Genetically Distinct Populations of the Secondary Symbiont Sodalis glossinidius

Genetic diversity among Sodalis glossinidius populations was investigated using amplified fragment length polymorphism markers. Strains collected from Glossina palpalis gambiensis and Glossina morsitans morsitans flies group into separate clusters, being differentially structured. This differential structuring may reflect different host-related selection pressures and may be related to the different vector competences of Glossina spp.     

Identification of Glossina palpalis gambiensis specific salivary antigens: towards the development of a serologic biomarker of human exposure to tsetse flies in West Africa

The saliva of blood sucking arthropods contains a number of pharmacologically active compounds that induce an antibody response in exposed human individuals. The objectives of the present study were (i) to assess the human IgG response directed against salivary antigens of Glossina palpalis gambiensis, the main vector of Trypanosoma brucei gambiense in West Africa, as a biomarker of human–tsetse contacts; and (ii) to identify specific salivary antigens. Immune reactivity of human plasma collected within active human African trypanosomiasis (HAT) foci (coastal Guinea), historical foci where tsetse flies are still present (South-West Burkina Faso) and a tsetse free area (Bobo-Dioulasso, Burkina Faso), was measured by ELISA against whole saliva extracts. In the active HAT foci and areas where tsetse flies were present in high densities, specific IgG responses were significantly higher (p < 0.0001) to those in Bobo-Dioulasso or in Loropeni, where tsetse flies were either absent or only present at low densities. Furthermore, 2D-electrophoresis combined with mass spectrometry enabled to reveal that several antigens were specifically recognized by plasma from exposed individuals. Among them, four salivary proteins were successfully identified (Ada, 5′Nuc, Ag5 and Tsgf1). These results represent a first attempt to identify Glossina salivary proteins or synthetic peptides to develop a standardized and specific biomarker of tsetse exposure in West Africa.     

Some changes in the flight apparatus of tsetse flies, Glossina morsitans and G. pallidipes, during maturation.

The residual dry weight of the thoracic cuticle of tsetse has been found to increase durint maturation and this finding affects the estimates of mitochondrial and contractile protein made by Bursell. The thoracic proline reserve was also found to increase during maturation, following much the same time course as that of the increases in contractile protein. The results are discussed with reference to the relevant published work on other insects.     

A novel vehicle-mounted sticky trap; an effective sampling tool for savannah tsetse flies Glossina morsitans morsitans Westwood and Glossina morsitans centralis Machado

BackgroundBlack screen fly round (BFR) is a mobile sampling method for Glossina morsitans. This technique relies on the ability of operator(s) to capture flies landing on the screen with hand nets. In this study, we aimed to evaluate a vehicle-mounted sticky panel trap (VST) that is independent of the operator’s ability to capture flies against BFR, for effective and rapid sampling of G. m. morsitans Westwood and G. m. centralis Machado. We also determined the influence of the VST colour (all-blue, all-black or 1:1 blue-black), orientation and presence of odour attractants on tsetse catch.Methodology/Principal findingsUsing randomised block design experiments conducted in Zambia, we compared and modelled the number of tsetse flies caught in the treatment arms using negative binomial regression. There were no significant differences in the catch indices of the three colour designs and for in-line or transversely oriented panels for both subspecies (P > 0.05). When baited with butanone and 1-octen-3-ol, VST caught 1.38 (1.11–1.72; P < 0.01) times more G. m. centralis flies than the un-baited trap. Attractants did not significantly increase the VST catch index for G. m. morsitans (P > 0.05). Overall, the VST caught 2.42 (1.91–3.10; P < 0.001) and 2.60 (1.50–3.21; P < 0.001) times more G. m. centralis and G. m. morsitans respectively, than the BFR. The VST and BFR took 10 and 35 min respectively to cover a 1 km transect.Conclusion/SignificanceThe VST is several times more effective for sampling G. m. morsitans and G. m. centralis than the BFR and we recommend its use as an alternative sampling tool.     

Does reproductive investment change with age in tsetse flies, Glossina morsitans morsitans (Diptera: Glossinidae)?

1. Viviparous insects such as tsetse ( Glossina spp.) provide unusual opportunities to compare age-related changes in the proportion of maternal resources transferred to offspring.
2. In laboratory populations of Glossina morsitans morsitans the survival of females was high for the first 60 days of adult life but declined rapidly thereafter.
3. Average longevity did not differ significantly between mated and unmated females (93·6 and 90 days, respectively).
4. Nutritional state in terms of fat content and residual dry mass did not decline with adult female age.
5. The fecundity of mated females was constant for the first 60 days of adult life and declined only slightly thereafter.
6. Offspring size did not change towards the end of the adult female lifespan and there was no evidence of an increase in the allocation of resources to reproduction in older females.
7. Results contrast with those obtained recently for vertebrates and may indicate that age-related changes in offspring size in Glossina are not adaptive, or that so few females reach old age under natural conditions that there is no selection for a strategy of terminal investment.     

Behavioral interactions and rhythms of activity of Glossina palpalis gambiensis and G. tachinoides (Diptera: Glossinidae) in forest gallery in the Burkina Faso

Glossina palpalis gambiensis and G. tachinoides are the main vectors of human and animal trypanosomoses in West Africa. In some parts of their distribution area, they co-exist in sympatry, but little is known about their interactions. This study aimed to explore their respective flight height and daily activity when co-existing or alone. Attractive targets were used, made of a black/blue/black cloth covered with adhesive film, so that all tsetse that landed were caught. The study was conducted in two areas in South Burkina Faso: Kartasso, upstream the Mouhoun river, where G. p. gambiensis is the only tsetse occurring; and Folonzo, on the Comoé river, where both species occur. Out of more than 3,800 tsetses caught in total, in Folonzo, G. tachinoides occurred at higher densities than G. p. gambiensis (84 vs 16% of the total densities). The mean height of capture was 55 cm for G. tachinoides, and 65 cm for G. p. gambiensis. As a comparison, in Kartasso where G. p. gambiensis is alone, the mean height of capture was 46 cm, these differences being statistically significant. In average, females were caught higher in altitude than males, and the two species showed a similar activity profile in the day. These results are discussed in the light of differences in the nature of the forest gallery, or possible interspecies competition behaviour in relation with their limited energy metabolism and flight capacities, or also with species differences in landing behavior, linked to host feeding detection. These observations have consequences on control tools releasing attractive odours, which may have contrasted efficacy depending of the flight height of the species.     

The interaction of dispersal and control methods for the riverine tsetse fly Glossina palpalis gambiensis (Diptera: Glossinidae): a modelling study

We used a spatial model of a riverine tsetse fly species Glossina palpalis gambiensis life cycle to investigate the interaction between their dispersal and three control methods and to document these interactions using sensitivity analyses. The model is currently limited to gallery forest habitat inhabited by Glossina palpalis gambiensis in the dry season in the sub-humid zone of West Africa. The control methods modelled were traps and targets (TT), insecticide-treated livestock (ITL), and the sterile insect technique (SIT). Both distance dispersed (up to 800 m) and percent of flies dispersing each day (up to 60 %) increased the efficiency of control by TT. Most of this increase occurred for low values of both distance dispersed and percent dispersing, but the increase continued up to the limits tried. The daily movement of cattle assisted the control program and when movement was considerable (up to 600 m daily) the effects were greater than the effects of tsetse dispersal. Random dispersal decreased aggregation and equilibrium population size, and thus also increased the efficiency of SIT. Dispersal that was mostly oriented towards clumps was of much less value for SIT but acted on TT and ITL similarly to random dispersal.     

Analysis of the mating activity of male tsetse flies Glossina m. morsitans and G. pallidipes in the laboratory

ABSTRACT. The responses of male Glossina morsitans morsitans West-wood and Glossina pallidipes Austen to freeze-killed females were examined in the laboratory. Analyses were performed using a specially designed, automated, computer-based, recording system. G. pallidipes were more active than G. m. morsitans , interacting with the female decoys twice as often. Interactions with the decoys divided broadly into short-stay (<60 s) and long-stay, full copulatory attempts. For G. m. morsitans 90% of interactions resulted in full copulatory attempts, the mean duration of which was >1 h. For G. pallidipes only 40% of interactions resulted in full copulatory attempts, the mean duration of which was 35 min. The initiation of interactions showed a clear V-shaped activity pattern in G. m. morsitans but in G. pallidipes only a morning peak was observed. In neither species was there a tendency for full copulatory responses to be initiated in any specific period of the diurnal activity pattern. The results indicate that the two species have very different mating systems, and represent an initial step in the quantification of these differences.     

Optimized simulation of the control of tsetse flies Glossina pallidipes and G. m. morsitans (Diptera: Glossinidae) using odour-baited targets in Zimbabwe

In 1984-1985 insecticide-treated targets were deployed in the 600-km2 Rifa Triangle, Zambezi Valley, Zimbabwe. Trap catches of Glossina pallidipes Austen were modelled using a function combining logistic growth with diffusive movement. A simulation routine was linked to a non-linear least-squares optimization programme and fits optimized with respect to population carrying capacities, rates of growth and movement, and to levels of imposed mortality. In March-September 1984, the overall additional mortality was 2% per day of adult female G. pallidipes, increasing thereafter to 8% per day, due to the deployment of more targets, the onset of the hot, dry season and the ground-spraying of the adjoining Zambezi escarpment with DDT. For G. m. morsitans Westwood the corresponding estimates were 1 and 2% per day. For both species, the deployment of four targets km(-2) in a closed population will ensure eradication. For G. m. morsitans a halving of target efficacy would reduce the killing rate to the point where eradication would be unlikely. Estimated daily displacements were c. 200 m for G. m. morsitans and 660 m for G. pallidipes. The lower rate for G. m. morsitans means that, while targets kill this species less effectively, re-invasion of cleared areas is slower. Targets do not markedly affect robust populations outside the deployment area. The Zambian tsetse population adjacent to the Rifa Triangle declined markedly during the experiment, however, suggesting that it is largely maintained by immigration. The methods developed here will be applied to data from other campaigns with the aim of improving the efficiency of tsetse control programmes.