Ultrastructure and Life Cycle of Merocinta davidii gen et sp. nov, a Dimorphic Microsporidian Parasite of Mansonia africana (Diptera: Culicidae) from Tanzania

Abstract

Mansonia africana larvae were sampled at three sites in NE Tanzania, between June and September 1987. At each site between 2.5 and 5.7% were infected with a multisporous microsporidian parasite. The ovoid spores measured 2.5 × 1.5 μm. Meronts were diplokaryotic with electron-dense, thickened unit membranes. Repeated division of the diplokarya gave rise to multinucleate plasmodia, the plasma membrane of which was entirely surrounded by two other membranes interpreted as host endoplasmic reticulum. Both membranes were studded with ribosomes. Meronts became ribbon-like before division, the endoplasmic reticulum dividing with the parasite. At the onset of sporogony the two nuclei of the diplokaryon separated and the electron-dense coat was sloughed off. Nuclear division and cytoplasmic division gave rise to uninucleate sporoblasts and spores. Adult M. africana collected at one of the three sites were infected with two diplokaryotic microsporidia, designated Type A and Type B, which differed only in the size of the spores. Spores of Type A measured 3.4 × 1.8 μm and those of Type B measured 6.6 × 2.9 μm; both types were binucleate. Type A infected 10.8 and Type B 5.8% of the adults collected. Mixed infections were not observed. In transovarial transmission trials, larvae were not successfully reared from adults infected with Type B. However, 11.3% of progeny from females infected with Type A exhibited multisporous microsporidian infections indistinguishable from those found in larvae collected at that site, showing that the multisporous parasite in larvae and the Type A infection of adults represent different stages in the life cycle of a single species. The morphology and life cycle of this microsporidian exclude it from all other related genera and it is attributed here to a new genus and given the name Merocinta davidii.