Spread of PI -Wolbachia infection in a population and its effect on the population sex ratio. A. Solid curve: Increase of PI-Wolbachia infection in a population over time where initially 1% of the females are infected, the transmission efficiency of the Wolbachia (α) is set at 95%; there is no cost of being infected (ω = 1). All females are mated. Dashed curve: The fraction of uninfected females that are the offspring of infected mothers. B. The ratio of females to males in the population over the generations. Values were derived using equation 5 from the text.