Teneral Glossina morsitans centralis were fed on the flanks of African buffalo, N'Dama or Boran cattle infected with Trypanosoma vivax IL 2337. The infected tsetse were maintained on goats and on day 25 after the infected feed, the surviving tsetse were dissected to determine the infection rates. The mean mature infection rates (% ± S.E.) in the tsetse fed on buffalo, N'Dama and Boran cattle were 34·3 ± 9·9, 33·7 ± 13·4 and 58·9 ± 7·1, respectively. Logistic regression analysis indicated that infection rates in the labrum and hypopharynx of the tsetse were significantly lower when fed on the infected buffalo or N'Dama than Boran cattle. Similarly, the risk of infection was significantly lower in male than female tsetse. When teneral G. m. centralis, G. pallidipes, G. p. gambiensis, G. brevipalpis and G. longipennis were fed simultaneously on either the buffalo cow, the N'Dama bull or the Boran steer infected with T. vivax IL 2337, the mature infection rates were higher in the two morsitans group than the two fusca group tsetse, whilst G. p. gambiensis was relatively refractory to the infection, irrespective of the host species on which they fed. Logistic regression analysis indicated that the infection rates in the labrum and hypopharynx were significantly different amongst the five tsetse species for each of the three infected host animals. Nevertheless, the trypanotolerant African buffalo and N'Dama cattle may serve as reservoirs of T. vivax infection as can trypanosusceptible Boran cattle.

Nine clones were derived from a drug-resistant Trypanosoma congolense stock (IL 2856) and characterized in mice for their sensitivity to isometamidium chloride and diminazene aceturate. All clones were derived from the stock without drug selection and expressed high levels of resistance to isometamidium chloride (50% curative dose [CD50] values ranging from 1·5 to 5·1 mg/kg) and intermediate to high levels of resistance to diminazene aceturate (CD50 values ranging from 5·1 to 21·0 mg/kg). By contrast, the isometamidium chloride and diminazene aceturate CD50 values for a drug-sensitive clone, T. congolense IL 1180, were 0·018 mg/kg and 2·3 mg/kg, respectively. For both drugs, there appeared to be significantly different levels in expression of drug resistance amongst the 9 clones derived from IL 2856. Isoenzyme analysis of 7 enzymes showed that all 9 clones expressed the same electrophoretic variants. Thus, all 9 clones were identical for these phenotypic markers. The clone which expressed the highest level of resistance to isometamidium in mice (IL 3270) was transmitted to Boran cattle via the bite of infected Glossina morsitans centralis. IL 3270 produced an infection rate in tsetse of 5·0%. The resulting infections in cattle were shown to be resistant to intramuscular treatment with 2·0 mg/kg isometamidium chloride and 14·0 mg/kg diminazene aceturate. This contrasts with doses of 0·25 mg/kg isometamidium chloride or 3·5 mg/kg diminazene aceturate which are deemed sufficient to cure fully sensitive infections. Finally, 9 clones (subclones) were derived from IL 3270 and characterized in mice for their sensitivity to isometamidium chloride. Seven of the subclones expressed a significantly lower level of resistance to isometamidium than the parental clone and amongst the subclones there was significant variation in resistance. Thus, expression of a high level of resistance to isometamidium appears to be unstable in the rodent host and at least a component of the genetic determinant(s) for this drug-resistant phenotype is (are) likely to be unstable.

A technique for infecting adult tsetse with an entomopathogenic fungus was developed and tested in the laboratory. A nitrocellulose filter membrane (Millipore) was used as substrate for retaining conidia after fitration, and a cylindrical plastic tube served as a chamber for the flies. The technique was designed to allow accurate estimation of inoculum on the substrate, thereby permitting comparison of virulence during the screening of fungal pathogens against tsetse flies. Glossina morsitans centralis adults were susceptible to Metarhizium anisopliae at all doses tested, and mortalities were dose dependent. No significant differences in mortalities were observed when flies were exposed for different durations to the pathogen. The number of conidia picked up by flies varied considerably with exposure time and concentration.

The infection rates and transmission characteristics of sterile male Glossina morsitans centralis, G. austeni and G. tachinoides for Trypanosoma vivax, T. congolense and T. brucei were studied. Teneral males were irradiated with 10 krad in a 137caesium source under ambient conditions. Five groups of teneral males of each species were sterilised by irradiation with 10 krad caesium source under ambient conditions and then fed for 3 days, together with five groups of normal males of their respective species, on three goats infected with T. vivax, T. congolense or T. brucei. The mean sterility rates were 98, 93 and 90% for G. m. cenlralis, G. austeni and G. tachinoides respectively. The mean percentage mature infection rates in the irradiated as against the controls of G. m. centralis, G. austeni and G. tachinoides were respectively 27.3 ± 9.5/27.7 ± 11.1, 4.0 ± 1.4/4.0 ± 2.6 and 14.8 ± 7.0/12.2 ± 5.0 for T. vivax; 24.6 ± 5.2/30.3 ± 4.3, 0.7/0.3 and 0.3/0.3 for T. congolense; and, 22.7 ± 2.6/23.4 ± 3.1, 1.1/0.2 and 0.7/1.7 for T. brucei. The transmission rates and frequency to A/J mice were very high and did not differ between the sterile and normal males. There was also no difference in the pattern of the diseases in the goats challenged by sterile or sexually fertile males of the three tsetse species. These results indicate that releases of sterile male tsetse in tsetse control programmes will potentially increase the trypanosomiasis risk in the affected area. Hence appropriate measures should be integrated in any SIR method of tsetse control campaign in order to provide adequate protection to man and his associated livestock.

The mating behaviour, with emphasis on the sexual maturation, of male tsetse, Glossina morsitans centralis (Machado, 1970) reared at the Uganda Trypanosomiasis Research Organization (UTRO) was investigated. Mating behaviour of 2–15 day-old males and 3-day-old females was observed. Three mating phases were recognized as courtship, mounting and genital interlocking (coupling), and jerking in most male flies tested.

The efficiency in coupling increased with age. Most males mounted the female mates after one attempt. The mating period in most males tested was between 1 and 3 hr, while the jerking period was on average 2.5 min. Most of the matings resulting in insemination lasted longer than 1 hr in all the age groups tested. The ability to inseminate and the degree of insemination produced by the older male flies were better than those by the younger ones. These results are discussed in relation to laboratory rearing of Glossina.