WOLBACHIA TRANSMISSION IN A NATURALLY BI-INFECTED DROSOPHILA-SIMULANSSTRAIN FROM NEW-CALEDONIA

Wolbachia are maternally-transmitted endocellular bacteria infecting s everal arthropod species. In order to study the possibility of Wolbach ia segregation in a naturally bi-infected host, isofemale lines from a bi-infected Drosophila simulans (Sturtevant) strain from Noumea (New Caledonia) were backcrossed using uninfected males carrying the same n uclear background. Uninfected males were used to avoid the cytoplasmic incompatibility syndrome (CI) associated with the presence of Wolbach ia in males. Each line was established using a female infected simulta neously by the two different Wolbachia variants wHa and wNo. The backc ross led to some individuals carrying only one type of infection being recovered among the progeny of the bi-infected foundress females. Rar ely, uninfected individuals were also recovered. Isolated for the firs t time in its natural host, wNo exhibited a significantly weaker CI ph enotype than the isolated wHa variant. Infection fate when backcross c onditions were relaxed varied depending on rearing conditions of the h ost. Under favourable conditions, the infection was generally maintain ed, while it was frequently lost under unfavourable conditions. This r esult probably reflects the direct fitness dependence of the symbiont on its host.