Self-propagating strategies, also known as self-sustaining strategies, rely on gene-drive systems that promote the spread and persistence of the transgene through populations of the same mosquito species. As opposed to the self-limiting strategy, the modifications in LM mosquitoes produced through self-propagating strategies are intended to be heritable and to spread through the target population and, thus, to persist in the ecosystem at least for the medium term. Hence, the objective of self-propagating strategies is the replacement of the non-modified mosquito population by the LM mosquitoes that have been modified to render them less capable of transmitting a disease. In a related approach, gene-drive systems may be used to promote the spread of a gene that confers a fitness load or a male bias in the offspring ratio. In this way, gene-drive systems may be used to suppress vector population sizes or induce a cascade of population crashes. An example of such a system is an X-shredding homing endonuclease gene (HEG) which can be driven into a population at the same time as biasing the offspring ratio towards males and hence potentially inducing an all-male population crash.