2026
The Nile tilapia is the latest fish species suggested as a target for control via gene drives. This species is native to the Nile and large parts of Africa, mainly north of the Congo basin, but has been introduced for aquaculture in other areas of Africa further south and on other continents, in many cases posing a threat to native biodiversity. One particular concern is the loss of genetic integrity of native tilapia species through inter-breeding with Nile tilapia. CRISPR-Cas9 based suppression gene drives are now proposed as a means of controlling invasive Nile tilapia populations to protect local biodiversity. A major issue acknowledged in the proposal is the obvious potential for gene drives to spread from the Nile tilapia to native tilapia species via inter-breeding, thus impacting some of the species they would be supposed to protect. To our knowledge, the Nile tilapia is the fourth species of fish put forward as a gene drive target alongside the sea-lamprey, the European carp and the lionfish.
2025
Concerns are being raised about plans to use gene drives to target whole groups of closely related species, a so called ‘target species complex.’ The malaria mosquito Anopheles gambiae is a high-profile gene drive target for suppression or eradication, and is known to be part of a group of at least nine closely related species which inter-breed – a so called species complex. This makes it likely that gene drives could spread to other mosquito species - including species that don’t spread human malaria- and impact them.
The idea of the ‘target species complex’ was proposed in 2023 by John Connolly and colleagues, who argue the concept allows impacts on non-vector species to ‘be recognised as a biological consequence of use of the gene drive intervention in a species complex’. They go on to argue that the transfer of a gene drive to non-vector species could be beneficial because they could ‘serve as ‘stepping stones’ for the gene drive to transfer to other sibling species that are themselves vectors’.
In a recent opinion piece in the Proceedings of the National Academy of Sciences, the evolutionary biologist Christopher Boete warns that the concept of the target species complex ‘risks reframing collateral impacts as intentional outcomes’. He argues that defining ‘…an entire species complex as the target sidesteps key ethical considerations, as it assumes that nonhuman organisms can be freely engineered and eliminated based solely on their genetic proximity to a target species…’ and thus disregards the intrinsic value of biodiversity.
A team funded by the Gates Foundation’s Transmission Zero project are proposing a ‘modular pathway towards deployment’ of gene drives to modify wild populations of Anopheles gambiae. Writing in the journal Nature the team describe a system where ‘effector and gene drive functions are separated into distinct genetic traits and strains’ (the ‘effector’ function in this case is a genetic modification expressing peptides which inhibit the growth of malaria parasites in the mosquito, while the ‘gene drive function’ is a separate modification in a different strain, and at a different genomic locus, which expresses Cas9). The idea would be to carry out test releases of these non-gene-drive mosquitoes – which are intended to reduce malaria transmission - and then to add in the gene drive function at a later stage through cross breeding with gene drive mosquitoes. In a separate paper in a different journal the same team report an invasive homing CRISPR-based gene drive system that could potentially be used for this purpose.
In the Nature paper the team state that ‘evaluating non-autonomous effector strains helps address elevated regulatory and containment requirements associated with autonomous gene drive systems’ - which may well indicate they hope that data obtained from releasing such transgenic non-gene drive strains might ease the regulatory pathway to releasing invasive gene drive systems at a later stage.
A recent study proposes that gene drives could be used to control mice in agricultural settings in Australia. Efforts to develop gene drives to eradicate mice have so far mainly been presented as a ‘conservation tool’ to address the harm caused by invasive mouse populations on islands, but this publication makes it clear that intentions for their use are much wider. The study from a team at the University of Adelaide present computer modelling which shows that their ‘t-CRISPR’ gene drive could be used as a pre-emptive control tool to reduce the economic impacts of mouse ‘plagues’ on agricultural crops. The study does not consider how the spread of gene drive mice would be prevented.
There have been other indications that conservation is not necessarily the main driver for research on gene drives in mice – for example as early as 2017 the Roslin Institute in the UK announced it was developing gene drives in mice for pest control. The potential use of the technology in agricultural settings has been alluded to in publications that focus primarily on conservation – for example the 2022 paper describing the t-CRISPR gene drive mentions the ‘loss of agricultural productivity’ caused by mice and other rodents.
On 18 August the government of Burkina Faso suspended all of Target Malaria’s operations in the country. This development followed a release of non-gene drive genetically modified mosquitoes on August 11. (see here for Target Malaria's statement, and here for news coverage)
A new study shows that the use of a 'leaky' promoter significantly affects the behaviour of a gene drive system. One of the most advanced gene drives systems targets a gene known as doublesex in the African malaria mosquito (Anopheles gambiae), and has caused concerns because it may spread uncontrollably. The Imperial College team, who produced this system, have now made a variant that should less rapidly, and which their models predict should be ‘self-limiting’. Compared to the original system, this variant uses a different promoter for expression of the Cas9 element of the drive, resulting in leaky somatic expression. In the original system female heterozygotes pass on the drive, however in the new variant the leaky Cas9 expression renders them sterile, leading to significant changes in how the drive behaves. We observe that these results raise questions about how mutations in promoters could lead to unexpected changes in gene drive behaviour after release in the wild.
The Asian malaria mosquito – Anopheles stephensi - is emerging as a significant target for ‘population suppression’ or eradication using gene drives. Teams at Peking University and the Pirbright Institute in the UK have developed separate gene drive systems in this species. Both these systems target the doublesex gene. Work in this species so far has aimed to replace wild populations with modified ones.
Rats are becoming a more serious prospect as a gene drive target. Researchers at the University of Adelaide for some time been modelling the use of gene drives for eradication of rat populations. Their new modelling work however draws on a pre-print publication from 2023 that describes a partially functional gene drive system in rats. This laboratory work has still not been published in a peer reviewed journal and so should be treated with caution. Nevertheless, it is significant because prior to it, the only reported gene drives constructed in mammals have been in mice.
Work is continuing by a group at Peking University to assess the feasibility of targeting ants with gene drives. Ants are a difficult target because of their colony structure and their chromosomal make up. The group’s new modelling study suggests that with multiple releases over long time-scales, gene drives could potentially be used against fire ants (Solenopsis invicta). They also propose targeting other ant species like crazy ants (Paratrechina longicornis) and Argentine ants (Linepithema humile).
- Remote Pacific islands are again being suggested as potential testing grounds for mosquito gene drives, because of their relative geographic isolation. Researchers have used genomic studies to investigate how Asian tiger mosquitoes (Aedes albopictus) have spread across the Pacific, and the extent of their ongoing movements. The study focussed on the Hawaiian Islands (USA), Guam (a US territory), and the Marshall Islands. The team believe their findings could help to develop ‘geographically isolated gene drives’, either using so called threshold dependent systems or by targeting ‘locally fixed alleles’ – an approach which is yet to be demonstrated in the laboratory.