Feeding behaviour of Glossina pallidipes and G-morsitans centralis on Boran cattle infected with Trypanosoma congolense or T-vivax under laboratory conditions

In field studies, tsetse flies (Diptera: Glossinidae) feed more successfull y on cattle infected with Trypanosoma congolense Broden (Kinetoplastida: Tr ypanosomatidae) than on cattle infected with T. vivax Ziemann or uninfected cattle. Here we describe the first laboratory investigation of this phenom enon. In the first experiment, caged Glossina pallidipes Austen were fed fo r 1 and 5 min on a Boran steer infected with T. congolense clone IL 1180 an d on an uninfected steer. Feeding success was recorded in this way five tim es over several weeks. The same protocol was subsequently used in three add itional experiments with the following combinations: G. pallidipes and a st eer infected with T. vivax stock IL 3913, G. morsitans centralis Machado an d a steer infected with T. congolense, and G. morsitans centralis and a ste er infected with T. vivax. The four experiments were replicated once, makin g eight experiments in total. In three experiments there was increased tset se feeding success, measured at 1 min, after a steer became infected (T. co ngolense, two experiments and T. vivax, one experiment). Analysis of all da ta combined found no significant differences in tsetse feeding success on t he different groups of cattle prior to infection, but after infection tsets e feeding success was significantly greater on the infected cattle (P < 0.0 01). Trypanosoma congolense infection led to a greater increase in tsetse f eeding success than T. vivax infection. The increase in feeding success was not related to changes in the level of anaemia, skin surface temperature o r parasitaemia. A possible explanation is the effects of trypanosome infect ion on cutaneous vasodilation and/or blood clotting in infected cattle. Whe n allowed to feed for 5 min, nearly all tsetse engorged successfully and ef fects of cattle infection on feeding success were not found.