Phenology of Stomoxyinae in a Kenyan forest.

The biology of nineteen taxa of African Stomoxyinae was studied during experiments with odour-baited Vavoua traps in Nairobi National Park, Kenya. Both male and female Stomoxys were captured in similar numbers with CO2 released at 2 l/min or octenol released at 2 mg/h. Some species of Haematobosca reacted synergistically to a combination of these attractants, producing large increases in catch. Stygeromyia and Rhinomusca responded only to CO2 and Prostomoxys did not respond to either bait. Many different activity patterns were documented in these genera, but most activity was concentrated just prior to sunset. For example, at peak densities nearly 1500 Stomoxyinae representing fourteen taxa were caught in a single trap between 18.00 and 19.00 hours. The Stomoxyinae community was exceptionally diverse when compared with other biting fly communities. Using data from traps set with different odour baits in the park forest, Shannon-Wiener diversity indices (H') varied from 2.5 to 2.8, and evenness (J') varied between 0.61 and 0.68. The Stomoxys population was extremely female-biased at the start of the rainy season, with species such as S. inornatus and S. boueti consisting of nearly 100% females. Sex ratios equalized when the first rainy-season generation emerged. population doubling times estimated from trap indices were approximately 12-16 days in two habitats (forest and riverine woodland).

Mechanical transmission of Trypanosoma spp. by African Stomoxyinae (Diptera: Muscidae).

Ten taxa of Stomoxyinae were tested for their ability to transmit Trypanosoma brucei, T. vivax, T. evansi and T. congolense to mice within 3 min of interrupted feeding on highly parasitaemic blood. T. brucei was the easiest parasite to transmit with an 11.5% success rate, followed by T. vivax at 3.4%, and T. evansi at 0.9%. T. congolense was not transmitted in 129 attempts. Stomoxys niger sspp. and four unstudied species (S. varipes, S. taeniatus, S. pallidus, Haematobosca squalida) were capable of transmitting trypanosomes mechanically.

Trypanosoma simiae in the white rhinoceros (Ceratotherium simum) and the dromedary camel (Camelus dromedarius).

Trypanosoma simiae was identified as the cause of a disease outbreak in dromedary camels (Camelus dromedarius) introduced to Tsavo East National Park, confirming the susceptibility of camels to this pathogen. T. simiae was also isolated from a new host, the white rhinoceros (Ceratotherium simum) through xenodiagnosis with a susceptible tsetse species (Glossina morsitans centralis). A white rhinoceros showed some evidence of anaemia and lymphopaenia when harbouring T. simiae, but did not suffer any long-term health effects.

Isolation of Trypanosoma spp. from wild tsetse flies through procyclic expansion in Glossina morsitans centralis.

Procyclic trypanosomes from wild tsetse flies were membrane-fed to Glossina morsitans centralis in order to develop an optimal technique for propagating field isolates. A 70% success rate was achieved in isolating Trypanosoma simiae and a variety of genotypes of T. congolense originating from G. pallidipes, G. brevipalpis and G. swynnertoni. Parasites matured into forms infective for mammals, and could be maintained by passage of gut forms to new groups of flies. In experiments with laboratory stocks, we also passaged immature gut infections of T. congolense and T. brucei from various tsetse species to G. m. centralis. The optimal technique was investigated for procyclic T. congolense through addition of various compounds to goat blood using G. m. centralis and G. m. morsitans as recipients. From these experiments, many approaches to procyclic expansion appeared possible. However, a simple and practical method based on the use of fresh goat blood for rapid feeding of G. m. centralis is recommended. Application of this technique should aid in the resolution of questions relating to the cryptic diversity of Nannomonas trypanosomes in diverse host and vector communities.

Dynamics of host blood effects in Glossina morsitans sspp. infected with Trypanosoma congolense and T. brucei.

The pattern of infection in Glossina morsitans morsitans and G. m. centralis membrane-fed on eland, buffalo or goat blood mixed with Trypanosoma congolense or T. brucei was studied from day 1 to day 10. Tsetse were initially permissive vectors, with most flies harbouring infections of 10(4)-10(5) parasites on day 3. However, after a second blood meal on day 3, flies cleared many infections, with G. m. morsitans clearing more infections than G.m. centralis. Infective feeds of goat blood consistently increased final infection rates by limiting the number of infections lost between days 3 and 6. In further experiments with G. m. morsitans only, this effect was replicated by feeding flies on erythrocytes but not on serum. These results suggest that compounds from some mammalian erythrocytes match the target specificity of G. m. morsitans midgut lectins and, hence, have a protective effect on trypanosome establishment in the fly.