Appendix 2: Potential gene

Disease applications

A gene drive could be used to reduce mosquito populations to help reduce the spread of diseases. Advances in gene editing techniques have led researchers to develop a CRISPR/Cas9 gene drive targeting a female sterility gene. This would lead to more male offspring than females and over multiple generations reduce Anopheles gambiae populations to a level where disease transmission of malaria is limited (Hammond et al., 2016). Although malaria is not an issue in Australia, we do experience other human viral diseases spread by mosquitoes, such as dengue and Ross River fever. Another approach is using Wolbachia, a bacterium which infects mosquitoes, to reduce transmission by Aedes aegypti populations in north Queensland, which is the main vector of dengue (Hoffmann et al., 2011).

Invasive species and the environment

A gene drive could be used to reduce the population of the non-indigenous mouse species Mus musculus on islands around the world, or specific to Australia, to reduce the population of black rats on Lord Howe Island. Introduced rodents can negatively affect an islands ecosystem by competing with native species and by destroying their habitats. Current efforts to eradicate invasive rodents have disadvantages including using toxic chemicals which can damage the environment or mechanical traps which don’t discriminate between introduced or native species. A gene drive targeting a sex determining gene, Sry, to produce more male offspring than females could lead to a reduced population of mice after several generations (Cocquet et al., 2012).

Rabbits are a classic example of an invasive, destructive species. Rabbits were introduced to Australia in 1859 for hunting but have since caused extensive damage, competing with livestock for grazing, spreading weeds, accelerating erosion and reducing biodiversity. It is estimated that rabbits cause A$200 million per year of economic damage.8 Efforts to control rabbit populations have had mixed success in the past, namely through biocontrol programs using viruses including Myxomatosis and calicivirus. However resistance has developed in some Australian rabbits meaning the rabbit population is again on the rise. A gene drive to reduce rabbit numbers would be highly beneficial for Australian farmers and our environment.

Agricultural applications

Gene drive systems hold a lot of promise in controlling agricultural invertebrate pests such as fruit flies, moth pests, thrips and mites. These pests tend to have short generation times and have often become problematical to control due to the evolution of resistance to widely-used pesticides such as pyrethroids and organophosphates.

Gene drive systems may also help deal with weed issues. For instance, Echinochloa colona, also known as barnyard grass or jungle rice, is a damaging weed for agricultural production in Australia. It particularly affects rice, sugarcane, maize, sorghum and summer fallow crops and since 2007 several populations have developed glyphosate resistance (Thai et al., 2012). Glyphosate is a herbicide commonly used to control weeds. The production of herbicide resistant crops have dramatically changed weed control practices. However after decades of herbicide use weeds are developing resistance, reducing the efficacy of glyphosate for weed control. A gene drive to reverse herbicide resistance would be valuable especially for Australian cotton farmers.

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