Fig. 3.

A single male-only release strategy with a weakly suppressed lethal cannot work. The examples shown are for a single (a) and two (b) male-only releases with 1:1 and 0.51:1 (introduced to wild-type) ratios, respectively (and relative fitnesses ${\varepsilon }_A=1={\varepsilon }_B$). Releases consist of individuals carrying weakly suppressed bisex lethals, however weakly suppressed female-only lethals give very similar results. In the single release case the first progeny produced are either transheterozygote (AaBb) or wild-type (aabb) since there are initially no transgenic females available for mating. The system therefore relies on transheterozygotes being able to exceed the release threshold which cannot happen for the release ratios considered in this work. If instead releases were made in the first two generations there will be double transgene homozygotes (AABB) available for mating with the initial progeny which allows the release threshold to be exceeded and thus transgenes to be introgressed.