The LAST Mile: Evaluating Genetic Biocontrol as a Supplemental Tool for Eradicating Invasive Rodents on Islands

Invasive rodents cause severe ecosystem degradation on islands and can be challenging to eradicate. Current best-practices rely on the application of toxic oral baits and have led to successful eradications and remarkable recoveries of native flora and fauna. Yet this single method is not universally applicable. Genetic biocontrol offers a suite of new solutions to potentially improve outcomes in the critical "last mile" of eradication. These approaches involve the release of genetically modified individuals of the target species to reduce population fitness over time. These include self-limiting approaches which require multiple releases and self-sustaining mechanisms (i.e., select gene-drive systems) which could theoretically collapse populations after a single release. While gene drive systems have received significant attention, their development in vertebrates remains technically challenging, and their ecological and regulatory implications are still in active debate. In contrast, some non-drive genetic biocontrol approaches, such as Y-linked editors, fsRIDL, and Gravid Lethal, offer self-limiting alternatives that may be more immediately deployable. These approaches could be used to supplement toxicant-based methods and may also have reduced environmental risks and regulatory barriers. To evaluate the potential of these tools, we developed an individual-based model simulating the eradication of house mice (Mus musculus) on a 125 ha island with an initial population of 11,000 individuals. We tested various combinations of genetic biocontrol release and effort strategies to understand tradeoffs between required effort and uncertainty for achieving successful eradication. Under certain effort strategies, we found that the Gravid Lethal approach performed the best, achieving eradication in < 2.3 years with intensive release effort and monitoring. Our findings suggest that integrating non-drive genetic biocontrol into adaptive management frameworks could enhance the effectiveness and feasibility of rodent eradication programs. These tools are not replacements for toxicants but may serve as critical supplements-particularly in the "last mile" of eradication.