How many species are infected with Wolbachia? Cryptic sex ratio distortersrevealed to be common by intensive sampling

Inherited bacterial symbionts from the genus Wolbachia have attracted much attention by virtue of their ability to manipulate the reproduction of thei r arthropod hosts. The potential importance of these bacteria has been unde rlined by surveys, which have estimated that 17% of insect species are infe cted. We examined whether these surveys have systematically underestimated the proportion of infected species through failing to detect the low-preval ence infections that are expected when Wolbachia distorts: the sex ratio. W e estimated the proportion of species infected with Wolbachia within Acraea butterflies by testing large collections of each species for infection. Se ven out of 24 species of Acraea were infected with Wolbachia. Four of these were infected with Wolbachia at high prevalence, a figure compatible with previous broad-scale surveys, whilst three carried low-prevalence infection s that would have had a very low likelihood of being detected by previous s ampling methods. This led us to conclude that sex-ratio-distorting Wolbachi a may be common in insects that have an ecology and/or genetics: that permi t the invasion of these parasites and that previous surveys may have seriou sly underestimated the proportion of species that are infected.