Population replacement and population suppression. (a) In population replacement strategies, the wild population is invaded by a heritable modification (e.g. transgene [5, 9] or pathogenic Wolbachia ) that reduces the vector competence of the mosquitoes that carry it. The number of competent vectors therefore declines, but the total number of (female) mosquitoes remains relatively constant, though possibly with some transient change during the invasion. (b) In contrast, a population suppression strategy aims to reduce the total number of vector mosquitoes. The two panels illustrate the changes in female population number and type over time for the two strategies. In both cases the situation will eventually reverse due to various pressures such as resistance, mutation, immigration, etc, unless some maintenance activities are undertaken.