Scientists have modeled a system that may be used to control mosquitoes and the diseases they transmit, without the use of pesticides. In the proposed system, mosquitoes are engineered to carry two genes the first gene causes males to transmit a toxin to females through their semen and the second gene, when expressed in females, makes them immune to this toxin. This research, published in the February 2011 issue of Genetics, describes a system that can be created using currently available molecular tools and could confine the spread of mosquitoes to isolated populations. It also allows the genes to be recalled if necessary.