Morgan_
Duckerz
You could kill off a species with a genetic killswitch. "Crispr gene drives" were a proposed solution to fighting Zika virus mosquitoes. Modify a mosquito to have a high chance of passing on a gene that causes infertility and with each successive generation the population dies out.
https://www.livescience.com/gene-drive.html
https://www.livescience.com/gene-drive.html