Nutritional levels of pregnant and postpartum tsetse Glossina pallidipes Austen captured in artificial warthog burrows in the Zambezi Valley of Zimbabwe

In Zimbabwe, female tsetse Glossina pallidipes Austen, collected from artificial warthog burrows and subjected to ovarian dissection and nutritional analysis, provide the first field estimates of resource allocation from mother to offspring across all of pregnancy. Approximately 45% of 1833 females captured are full‐term pregnant on entering the burrow. The remainder presumably use burrows as refuges at temperatures >32 °C. Maternal residual dry weight (RDW) increases by 1.5 mg after the first feed post‐larviposition but, thereafter, only by 1.4 mg by 90% of pregnancy completion. Uterine RDW changes little by 60% of pregnancy completion but increases by >6 mg by parturition. Between the times of 5% and 90% pregnancy completion, maternal RDW is approximately constant: it then declines 2.8 mg by parturition, balancing larval gains of 2.6 mg. Mothers accumulate 6.3 mg of fat in the first 80% of pregnancy, while uterine fat increases by only 0.8 mg. Thereafter, by parturition, larval fat increases by 4.1 mg, whereas maternal fat declines by 3.3 mg. The larva deposited is 5% heavier than its mother and has 52% more fat. RDW and fat levels, corrected for fly size and haematin, are 1 and 2 mg, respectively, lower in females from traps than those from burrows. Burrow catches provide an improved picture of tsetse pregnancy dynamics, highlighting a reproductive strategy involving resource commitment to the larva being delayed until late pregnancy when sufficient stores guarantee viable pupal production. Larval development in tsetse starts significantly later than the analogous changes during pregnancy in two mammals and two viviparous fish.     

Behaviour of tsetse flies (Glossina) in host odour plumes in the field

ABSTRACT. In Zimbabwe, studies were made of the responses of Glossina pallidipes Austen and G.morsitans morsitans Westwood to artificial host odour using an incomplete ring of electrocuting nets. In a plume of synthetic host odour tsetse flew generally upwind, with 50–60% flying within 35^o of due upwind. More than 80% of tsetse flew at < 50 cm above ground level. Upon losing contact with odour they executed a reverse turn within about 2 m, and upon regaining contact they turned upwind. There were no clear differences in the responses of G.m.morsitans and G.pallidipes. Using electrocuting nets lying horizontally on the ground it was found that tsetse landed in the vicinity of the odour source, the propensity to land being greater for G.pallidipes than for G.m, morsitans , greater for immature than mature flies, and greater for males than females.     

Use of fluorescent pigments for the automatic marking of tsetse flies in traps

A means of contaminating tsetse flies in the field with fluorescent pigment powders has been developed, using pigment in open-ended plastic chambers at the cage position on traps. Glossina pallidipes Austen and G.morsitans morsitans Westwood passed rapidly through the chambers, and on exit were contaminated with consistent doses of powder: about 90 micrograms/fly when powder was presented on the chamber roof and about 28 micrograms/fly when powder was presented on the chamber floor. The technique automatically marks tsetse flies with pigment, cheaply, simply and with the minimum imposition of stress and is expected to be particularly useful in ecological studies. Its potential for marking other biting flies is discussed.     

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.     

Prospects of a fungus-contamination device for the control of tsetse fly Glossina fuscipes fuscipes

The prospects of the fungus Metarhizium anisopliae (Metsch.) Sorok. applied in contamination devices (Cds) to control tsetse fly Glossina fuscipes fuscipes Newstead was tested in a field experiment in Lake Victoria from 2 March 1999 to 31 August 2000. One hundred and sixty pyramidal traps mounted with Cds were deployed along the lakeshore and rivers on Mfangano Island. Contamination devices were loaded with 1.5-2.0 g of dry conidia/Cd. On the second island, Nzenze Island, four pyramidal traps fitted with plastic bags were deployed and served as the conventional 'trap and kill' population suppression method. A third island, Ngodhe Island, remained untreated and served as a control. Cds were recharged monthly with fresh conidia; plastic bags were also changed monthly. The apparent changes in population density were monitored weekly using biconical traps set at random on the three islands. To assess the incidence of M. anisopliae in tsetse flies on Mfangano Island, flies captured during monitoring were maintained in the laboratory and their mortality recorded. Fly population was reduced to 82.4 and 95.8% relative to untreated control on Mfangano and Nzenze islands, respectively, during the experimental period. Compared to the fungus-treated island, the number of flies caught in monitoring traps increased considerably in 'trap kill' treatment at 5 months after the treatments were removed. The incidence of M. anisopliae in fly populations was low during the 12 weeks following the initiation of the experiment but increased afterward until termination of the treatment. M. anisopliae could still be recovered from fly populations at 3 months after termination of the treatment, although the incidence was low. The results of this study have shown that application of M. anisopliae in a contamination device can suppress the population of G. fuscipes fuscipes comparable to the 'trap and kill' technology.     

Shoo fly, don't bother me! Efficacy of traditional methods of protecting cattle from tsetse

Studies were made of the efficacy of using smoke and housing to protect cattle from tsetse (Diptera: Glossinidae) in Zimbabwe. The efficacy of smoke was assessed by its effect on catches in Epsilon traps baited with a blend of acetone, 1-octen-3-ol, 4-methylphenol and 3-n-propylphenol. The efficacies of different types of kraal (enclosure) were gauged according to the catches of electrocuting targets (E-targets), baited with natural ox odour, placed within various designs of kraal. Smoke from burning wood (Colophospermum mopane) or dried cow dung reduced the catch of traps by approximately 50-90%. Kraals with a continuous wooden or netting wall, 1.5 m high, reduced catches of E-targets by approximately 75%. Arrangements of electric nets were used to assess the numbers of tsetse attacking live cattle within kraals and/or near sources of smoke. The results confirmed findings with traps and E-targets: kraals reduced the numbers of tsetse that fed by approximately 80% and smoke reduced the numbers attracted by approximately 70%; the use of both reduced overall attack rates by approximately 90%. The inclusion of 4-methylguaiacol, a known repellent for tsetse and a natural component of wood smoke, halved the catches of traps and E-targets and the numbers of tsetse attacking cattle. The practical benefits and difficulties of using repellents and/or housing to manage trypanosomiases are discussed.     

Comment on Barclay and Vreysen: Published dynamic population model for tsetse cannot fit field data

The structure, and assumed parameter values, of a recent dynamic population model for tsetse (Diptera: Glossinidae) render it unable to fit published data on tsetse control programs using odor-baited targets, insecticide-treated cattle and the sterile insect technique (SIT). The underlying problem is a mismatch between the small size of the mapped cells (1 ha) and the long time-step, which allows flies to move only once every 5 days, and then only to an adjacent cell. Assumed rates of tsetse dispersal and killing by odor-baited targets are consequently at least an order of magnitude lower than observed in the field. Suggestions that Glossina pallidipes could be eradicated more rapidly with SIT, than using hundreds of targets per km², is contradicted both by the field data and by three other independent modeling studies.     

Conclusions from a dynamic population model for tsetse: response to comments

The critique by Hargrove et al. (Popul Ecol, 2011) of our recently published paper on a tsetse population model (Barclay and Vreysen in Popul Ecol 53:89–110, 2011) has made some good points but has also misinterpreted the intent of some of our results as we presented them. Hargrove et al. rightly say that there is a mismatch between the size of the unit cells in the model (1 ha) and the iteration rate of the model (every 5 days), yielding too low a dispersal rate to simulate reality. However, they have misconstrued several of our results that we presented as examples to imply that those results were a necessary condition for control of tsetse, especially using traps and targets.