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.     

Characterization of microsatellite markers in the tsetse fly, Glossina pallidipes (Diptera: Glossinidae)

Glossina pallidipes is a vector of African trypanosomiasis. Here we characterize eight new polymorphic microsatellite loci in 288 G. pallidipes sampled from 12 Kenya populations. The number of alleles per locus ranged from four to 36 with a mean of 20.5 +/- 10.1. Expected single locus heterozygosities varied from 0.044 to 0.829. Heterozygosity averaged 0.616 +/- 0.246. No linkage disequilibrium was found. We also report results in eight other tsetse species estimated by using the primers developed in G. pallidipes. The primers worked best in G. swynnertoni and G. austeni and worst in G. m. morsitans and G. m. submorsitans.     

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.     

Genetic variation in Glossina brevipalpis, G.longipennis and G.pallidipes, and the phenetic relationships of Glossina species

Glossina brevipalpis Newstead, G.longipennis Corti, and G.pallidipes Austen maintained at ILRAD, Nairobi, Kenya, were examined for genetic variation of fourteen enzyme loci, using polyacrylamide gel electrophoresis. G.brevipalpis had six polymorphic loci, an average of 1.46 effective alleles per locus and a mean heterozygosity per locus of 20.0 +/- 7.1%. The figures for the same parameters in G.longipennis were 3, 1.16 and 8.2 +/- 4.9%, and for G.pallidipes the figures were 7, 1.40 and 22.3 +/- 6.3%. Seven rare alleles were lost from the G.brevipalpis colony during a 1-year period, but no statistically significant changes were observed in the genetics of the colony during this period. Using allele frequency data for ten of the enzymes studied, and frequencies for these enzymes in other taxa, a phenogram was constructed that indicated that the subgenus Austenina (i.e. the fusca group) is the oldest of the three subgenera within the genus Glossina, and that the subgenus Glossina s.str. (i.e. the morsitans group) may be paraphyletic.     

Genetics of hybridization of Glossina swynnertoni with Glossina morsitans morsitans and Glossina morsitans centralis

Abstract Reciprocal crosses were performed with Glossina swynnertoni and Glossina morsitans morsitans and with G. swynnertoni and Glossina morsitans centralis , using strains that carried marker genes in all three linkage groups. Glossina swynnertoni males can inseminate, but not fertilize, G.m.morsitans; all other crosses produced some fertile females. Hybridization did not cause sex ratio distortion among F_{ flies. Most F and backcross females were fertile, but all F, males were sterile. Sterility among backcross males was also high (99% in BXj, 85% in Bx₂, and about 50% in Bx₃ to Bx₅). Chromosome transmission by hybrid females usually conformed to Mendelian expectations, but genetic recombination was lower than observed in G.m.morsitans. The reduction in fertility among backcross females was not associated with heterozygosity in any linkage group. Sterility among hybrid and backcross males was associated with heterozygosity of sex chromosomes and probably autosomes. The results support the systematic placement of G.swynnertoni closer to G.mxentralis than to G.m.morsitans.     

Responses of tsetse flies (Glossina spp.) to compounds on the skin surface of an ox: a laboratory study

The behaviour of male Glossina morsitans morsitans Westwood and Glossina pallidipes Austen (Diptera: Glossinidae) alighting on targets with or without ox sebum was compared. The presence of ox sebum did not increase significantly the number of flies alighting on the target in either species. However, after contact with the sebum coated target, both species showed an increase in flight activity, and G. m.morsitans showed a greater tendency to return to the target. This behaviour resulted in a number of short flights which may reflect the search for a feeding site on a host. The duration of each visit to the target was significantly reduced when sebum was present for G. m. morsitans but not for G. pallidipes. This is explained by documented differences in the resting behaviour of the two species which shows that G. m. morsitans normally rests for longer periods on the surface of an untreated black target than does G. pallidipes. Other experiments showed that the presence of sebum elicited a probing response in G. m. morsitans and G. pallidipes. The results are discussed with reference to the possible use of host sebum to improve trap catches in the field.     

A comparison of African buffalo, N''Dama and Boran cattle as reservoirs of Trypanosoma congolense for different Glossina species

Teneral Glossina morsitans centralis Machado were fed on the flanks of the African buffalo (Syncerus caffer Sparrman), N'Dama (Bos taurus L.) or Boran (Bos indicus L.) cattle infected with Trypanosoma congolense Broden. The infected tsetse were maintained on rabbits and on day 30 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean infection rates (% +/- SE) in the midgut of tsetse fed on buffalo, N'Damas and Borans were 23.5 +/- 3.3, 31.6 +/- 2.7 and 33.7 +/- 4.6, respectively. The differences were not significant. However, the mean mature infection rate in tsetse fed on the buffalo (13.2 +/- 2.1%) was significantly lower compared to the rates in tsetse fed on the N'Dama (20.4 +/- 1.4) or the Boran cattle (21.4 +/- 1.1). When groups of teneral G.m.centralis, G.pallidipes Austen, G.p.gambiensis Vanderplank, G.f.fuscipes Newstead, G.brevipalpis Newstead and G.longipennis Corti were fed simultaneously on either an infected buffalo, an N'Dama or a Boran steer, the mature infection rates ranged from 0 to 16.1%. Irrespective of the host species used, the T.congolense infection rate was highest in G.m.centralis, lowest in the palpalis and fusca group tsetse, with G.pallidipes being intermediate. Nevertheless, the trypanoresistant African buffalo and N'Dama may serve as reservoirs of T.congolense as can trypanosusceptible Boran cattle.     

The effects of temperature, body mass and feeding on metabolic rate in the tsetse fly Glossina morsitans centralis

Abstract.  Metabolic rate variation with temperature, body mass, gender and feeding status is documented for Glossina morsitans centralis . Metabolic rate [mean ± SE; VCO₂= 19.78 ± 3.11 μL CO₂ h⁻¹ in males (mean mass = 22.72 ± 1.41 mg) and 27.34 ± 3.86 μL CO₂ h⁻¹ in females (mean mass = 29.28 ± 1.96 mg) at 24 °C in fasted individuals] is strongly influenced by temperature, body mass and feeding status, but not by gender once the effects of body mass have been accounted for. A significant interaction between gender and feeding status is seen, similar to patterns of metabolic rate variation documented in Glossina morsitans morsitans . Synthesis of metabolic rate-temperature relationships in G. m. centralis , G. m. morsitans and Glossina pallidipes indicate that biting frequency as well as mortality risks associated with foraging will probably increase with temperature as a consequence of increasing metabolic demands, although there is little evidence for variation among species at present. Furthermore, metabolic rate–body mass relationships appear to be similarly invariant among these species. These data provide important physiological information for bottom-up modelling of tsetse fly population dynamics.     

Increased expression of unusual EP repeat-containing proteins in the midgut of the tsetse fly (Glossina) after bacterial challenge

Proteins containing a glutamic acid-proline (EP) repeat epitope were immunologically detected in midguts from eight species of Glossina (tsetse flies). The molecular masses of the tsetse EP proteins differed among species groups. The amino acid sequence of one of these proteins, from Glossina palpalis palpalis, was determined and compared to the sequence of a homologue, the tsetse midgut EP protein of Glossina m. morsitans. The extended EP repeat domains comprised between 36% (G. m. morsitans) and 46% (G. p. palpalis) of the amino acid residues, but otherwise the two polypeptide chains shared most of their sequences and predicted functional domains. The levels of expression of tsetse EP protein in adult teneral midguts were markedly higher than in midguts from larvae. The EP protein was detected by immunoblotting in the fat body, proventriculus and midgut, the known major immune tissues of tsetse and is likely secreted as it was also detected in hemolymph. The EP protein was not produced by the bacterial symbionts of tsetse midguts as determined by genome analysis of Wigglesworthia glossinidia and immunoblot analysis of Sodalis glossinidius. Bacterial challenge of G. m. morsitans, by injection of live E. coli, induced augmented expression of the tsetse EP protein. The presence of EP proteins in a wide variety of tsetse, their constitutive expression in adult fat body and midguts and their upregulation after immunogen challenge suggest they play an important role as a component of the immune system in tsetse.     

Reproductive rates of tsetse flies in the field in Zimbabwe

Abstract. Tsetse flies Glossina morsitans morsitans Westwood and G. pallidipes Austen were marked and released within 12 h of emergence at Rekomitjie Research Station, Zambezi Valley, Zimbabwe, and on Redcliff Island, Lake Kariba. Ovarian dissections were performed on recaptured flies and on wild collected samples. At Rekomitjie >90% of female G. m. morsitans were inseminated by age 4 days and G. pallidipes by 7 days. For both species at both sites the length of the largest oocyte, for flies in ovarian category zero, increased approximately linearly for about the first 6 days and was ovulated at c. 6–8 days. The largest oocyte grew significantly more slowly in later cycles. For G. m. morsitans , but not for G. pallidipes , the rate increased with temperature; the rates were always higher than observed in the laboratory. At Rekomitjie, for both species and at a mean screen temperature of 22C, the first larva was produced at c. 18 days and subsequent larvae at 11–day intervals; the intervals decreased with temperature by c. 0.5 days/C. On Redcliff Island the intervals for both species were 2 days shorter than at Rekomitjie at any given screen temperature and were sometimes as short as 7 days. The length of the larva in utero increased exponentially during pregnancy.     

Survival and reproductive performance of female Glossina morsitans morsitans when maintained on the blood of different species of wild mammals

A study was carried out to determine the effect on the reproductive performance of female Glossina morsitans morsitans Westwood when allowed to feed, in vitro, for 63 days on fresh defibrinated blood of buffalo, bushbuck, cattle, eland, oryx, warthog, waterbuck or wildebeest. There were marginal differences in the survival and reproductive performance between eight different groups of tsetse, 200 per group, when fed on the blood of these mammalian species. When allowed to feed for 14 consecutive days on the blood of buffalo, wildebeest or warthog, the mean number of feeds were 6.2 +/- 0.3, 6.5 +/- 0.3 and 6.3 +/- 0.3, respectively. The mean weight of the bloodmeal taken also did not differ significantly between these three groups. Whereas the protein patterns of the blood plasma of the above eight host animals were different, the protein patterns of the haemolymph from tsetse fed on the blood of these hosts were identical. It is thus concluded that the preference shown by tsetse for some mammalian species investigated here may not be based on any aspect of the nutritional value of their blood.     

Activation of three species of tsetse (Glossina spp.) in response to host derived stimuli

Recordings were made of the activation of hungry Glossina morsitans morsitans Westwood, G. pallidipes Austen, and G. austeni Newstead in response to odours from ox breath and ox urine, and a moving visual stimulus, in a wind tunnel. The spontaneous activity of G.m.morsitans was very low (less than 4% of males and 2% of females active per min during control periods). That of G.austeni and G.pallidipes was in the region of 20% except for G.pallidipes females when in excess of 40% were active during control periods. Addition of ox urine odours to the airstream had no effect on activity in any of the species investigated but addition of ox breath odours to the airstream significantly increased activity of G.pallidipes and of G.m.morsitans, although for the latter only approximately 12% of flies were active. For G.austeni the addition of ox breath odours resulted in a significant increase in activity of females but not of males. The moving visual stimulus resulted in a significant increase in the activity of both sexes of G.austeni and G.m.morsitans but no change in the activity of G.pallidipes. The low level of spontaneous activity and the low response to ox breath odours in a strain of G.m.morsitans maintained in the laboratory since 1969 was compared with a new colony of this species which originated from puparia collected in Zimbabwe in 1991. No differences in either spontaneous activity or the response to ox breath odour was recorded, but females from the new colony were significantly more responsive to a moving visual stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationships between host blood factors and proteases in Glossina morsitans subspecies infected with Trypanosoma congolense

Abstract. Host blood effects on Trypanosoma congolense establishment in Glossina morsitans morsitans and Glossina morsitans centralis were investigated using goat, rabbit, cow and rhinoceros blood. Meals containing goat erythrocytes facilitated infection in G. m. morsitans , whereas meals containing goat plasma facilitated infection in G. m. centralis. Goat blood effects were not observed in the presence of complementary rabbit blood components. N-acetyl-glucosamine (a midguMectin inhibitor) increased infection rates in some, but not all, blood manipulations. Cholesterol increased infection rates in G. m. centralis only. Both compounds together added to cow blood produced superinfection in G. m. centralis , but not in G. m. morsitans. Midgut protease levels did not differ 6 days post-infection in flies maintaining infections versus flies clearing infections. Protease levels were weakly correlated with patterns of infection, but only in G. m. morsitans. These results suggest that physiological mechanisms responsible for variation in infection rates are only superficially similar in these closely-related tsetse.     

Genetic relationships between subspecies of the tsetse fly Glossina morsitans inferred from variation in mitochondrial DNA sequences

A 750 base pair segment of DNA from the tsetse fly Glossina morsitans morsitans was isolated by means of molecular cloning. It was shown by DNA hybridization to have substantial sequence homology with a defined region of the mitochondrial genomes of several Drosophila species. When used as a probe against DNA prepared from single tsetse flies, the cloned sequence revealed local restriction site variation between members of the G. morsitans subspecies complex. This feature was used to demonstrate maternal inheritance of the sequence in progeny of hybrid crosses and to assemble comparative restriction maps for a 3-kilobase segment of each mitochondrial genome. The data obtained from these exercises point to a higher genetic identity between G. m. morsitans and G. m. centralis than between either form and G. m. submorsitans.     

Labellar microstructure in tsetse flies (Glossinidae)

Abstract. Stereo-electron micrographs of the labellar armature of eleven of the commoner species of Glossina indicate that the most generalized type of labellum occurs in G.palpalis , a species which feeds on a wide range of animals. The species of the fusca and morsitans groups show independently evolved adaptations to feeding on bovids and other mammals. G.brevipalpis has a generalized type of labellum with special adaptations to feeding on hippopotamus and suids and the labellum of G.longipennis is specialized for feeding on elephant and rhinoceros. The range of labellar structure within Glossina is not entirely consistent with the traditional classification of the genus into fusca, palpalis and morsitans species-groups.     

Mapping tsetse habitat suitability in the common fly belt of Southern Africa using multivariate analysis of climate and remotely sensed vegetation data

Abstract The distribution of Glossina morsitans centralis, Glossina morsitans morsitans and Glossina pallidipes are described in part of southern Africa, using a range of multivariate techniques applied to climate and remotely sensed vegetation data. Linear discriminant analysis is limited in its predictive power by the assumption of common co-variances in the classes within multivariate environment space. Maximum likelihood classification is one of a variety of alternative methods that do not have this constraint, and produce a better prediction, particularly when a priori probabilities of presence and absence are taken into account. The best predictions are obtained when the habitat is subdivided, prior to classification, on the basis of a bimodality detected on the third component axis of a principal component analysis. The results of the predictions were good, particularly for G.m.centralis and G.m.morsitans , which gave overall correct predictions of 92.8% and 85.1 %, with a Kappa index of agreement between the predion and the training data of 0.7305 and 0.641 respectively. For G.pallidipes , 91.7% of predictions were correct but the value of Kappa was only 0.549. Very clear differences are demonstrated between the habitats of the two subspecies Gmxentralis and G.m.morsitans.     

Comparative study on the infection rates of different laboratory strains of Glossina species by Trypanosoma congolense

Teneral Glossina morsitans centralis Machado, G.austeni Newstead, G.palpalis palpalis Robineau-Desvoidy, G.p.gambiensis Vanderplank, G.fuscipes fuscipes Newstead, G.tachinoides Westwood and G.brevipalpis Newstead, from laboratory-bred colonies, were fed at the same time on the flanks of ten goats infected with Trypanosoma congolense Broden isolated in Tanzania or in Nigeria. The seven tsetse species were infected over the range 0.3-49.2%. Survival of both T.congolense isolates was best in G.m.centralis, poorest in G.austeni and the four palpalis group tsetse, with G.brevipalpis intermediate. It is suggested that there are differences in the gut of different laboratory-bred cultures of Glossina Westwood species and subspecies such that T.congolense parasites can survive better in the gut of some than in others and undergo cyclical development to metacyclics in the hypopharynx.     

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.     

Effects of age, sex and hunger on the antennal olfactory sensitivity of tsetse flies

Abstract 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.     

Univariate analysis of tsetse habitat in the common fly belt of Southern Africa using climate and remotely sensed vegetation data

Abstract Tsetse are vectors of trypanosomes that cause diseases both in humans and livestock. Traditional tsetse surveys, using sampling methods such as Epsilon traps and black screen fly rounds, are often logistically difficult, costly and time-consuming. The distribution of tsetse, as revealed by such survey methods, is strongly influenced by environmental conditions, such as climate and vegetation cover, which may be readily mapped using satellite data. These data may be used to make predictions of the probable distribution of tsetse in unsurveyed areas by determining the environmental characteristics of areas of tsetse presence and absence in surveyed areas. The same methods may also be used to characterize differences between tsetse species and subspecies. In this paper we analyse the distribution of Glossina morsitans centralis, Glossina morsitans morsitans and Glossina pallidipes in southern Africa with respect to single environmental variables. For G.m.centralis the best predictions were made using the average NDVI (75% correct predictions; range > 0.37) and the average of the maximum temperature (70% correct predictions; 27.0–29.2°C). For G.m.morsitans the best prediction was given by the maximum of the minimum temperature (84% correct predictions; range > 18.8°C), and for G.pallidipes , also by the maximum of the minimum temperature (86% correct predictions; range > 19.6 °C). The following paper compares a range of multivariate techniques for making predictions about the distribution of these species in the same region.