A mite species that consists entirely of haploid females

The dominance of the diploid state in higher organisms, with haploidy gener ally confined to the gametic phase, has Led to the perception that diploidy is favored by selection. This view is highlighted by the fact that no know n female organism within the Metazoa exists exclusively (or even for a prol onged period) in a haploid state. We used fluorescence microscopy and varia tion at nine microsatellite Loci to show that the false spider mite, Brevip alpus phoenicis, consists of haploid female parthenogens. We show that this reproductive anomaly is caused by infection by an undescribed endosymbioti c bacterium, which results in feminization of haploid genetic males.