Influence of the intensity of parasitaemia on the vectorial competence of Glossina morsitans morsitans Westwood, 1850 (Mall) infected with Trypanosoma (Nannomonas) congolense IL 1180

Two groups of teneral flies (aged less than 32 hours) of Glossina morsitans morsitans (Mall) were fed separately on two rats that had been infected wi th Trypanosoma (Nannomonas) congolense IL 1180, among which one had a low p arasitaemia (antilog 5.4-5.7) and the other a high parasitaemia (antilog 7. 8-8.1). Following to the two modes of parasitaemia, variations of the procy clic indexes were found between males and females. When both sexes were con sidered, it was found that the intestinal infection rate was relatively hig her in the flies that were fed on the rat with a low parasitaemia than in t hose fed on the rat with a high parasitaemia. Although no significant diffe rences in metacyclic indexes were observed between sexes, the mature infect ion rate was most pronounced in the flies that were fed on the rat with hig h parasitaemia. When both sexes were considered, the vectorial competence ( VC) reached 0.5532 and 0.5521 in the flies that had been fed on the rats wi th low and high parasitaemia, respectively. The VC of the two modes of infe ctious feeding was not significantly different. However, when considering t he parasitaemia of antilog 5.4-5.7, the VC was relatively more important in the females than in the males. No significant difference in VC was detecte d between sexes when considering the antilog 7.8-8.1 parasitaemia. it was f ound that there is discrepancy in the way the metacyclic infection and the VC evolve in relation to the procyclic infection, suggesting that the inten sity of the parasitaemia only influences the intestinal stage.