Expert response from Tony Shelton
Tuesday, 19/04/2016 14:21
Sorry, but we need to modify your question a bit. GMOs (genetically modified organisms) is a term most scientists like to avoid since many species have been “modified” by humans to a greater or lesser extent since the beginning of agriculture. We prefer to use the term genetically engineered (GE) since it describes a targeted genetic change to an organism so that it produces a novel trait, such as a plant that is resistant to an insect or pathogen, or more recently, an insect pest engineered to control its own species.
In that context, yes, GE organisms display great potential to be applied against invasive and pestiferous species around the globe. GE technologies can be used to turn the mating behavior of a pest against itself, an idea that was promoted by Rachel Carson in her 1962 book, Silent Spring. In principle, scientists can genetically engineer a pest in the laboratory to carry a lethal gene and then release the organism into the wild. When the GE ‘pest’ meets and mates with a wild pest, it will pass on its lethal gene to the next generation, which will not survive. If you release enough of these GE pests into the wild in a confined area they can reduce, or even eradicate, a wild pest population just by mating with a sufficient number of individuals in the population. An earlier example of this approach (the Sterile Insect Technique, SIT) has successfully eradicated several important insect pests including the screwworm, a pest of livestock in the Americas. In existing SIT programs sterility is induced by radiation, but radiation produces random changes in the insect’s chromosomes. So, in addition to creating sterility, the fitness of the insect may be reduced (e.g., it may not fly well or be very competitive to mate with females.) Genetic engineering allows sterility to be achieved while minimizing such negative effects, and therefore can be much more effective at pest population control.
Rodents such as rats and mice represent the most promising vertebrate target for these genetic control strategies. Early stage research has been conducted into developing genetic control strategies in mice and projects are ongoing in developing these technologies for control of invasive rats on islands.
Considerable research has been devoted to developing and testing GE insect pests carrying these lethal genes. The species which have been targeted are primarily ‘commercial pests’ i.e. those which pose threats to agriculture or human health. Two GE insects are being tested against invasive pests: the diamondback moth in New York State and the dengue fever mosquito in South America, South-East Asia and the Caribbean. With GE mosquitoes, field trials have shown that they are able to reduce wild populations by up to 95 percent in a single year - a significant advance over chemical insecticides. Researchers are now turning their attention to invasive insect species which impact biodiversity, for example the mosquito which transmits avian malaria and has devastated Hawaii’s native honeycreeper birds. These GE technologies are appropriate for use against invasive species because they are highly effective at eradicating small and difficult to reach pest populations. They are also extremely target-species specific and environmentally friendly. For example, a GE insect will only mate with its own species and therefore, unlike most insecticides, will not affect beneficial insects such as pollinators. Other approaches, in contrast to adding a lethal trait into an insect population, are also being developed. For example, research has also demonstrated that mosquitoes can be engineered so they are not able to transmit pathogens that cause human or animal diseases. Thus, while the insect species will remain in the ecosystem it will no longer be a threat.
Development of these technologies for vertebrate pests has lagged behind insects. This is because vertebrates have longer life-cycles and are more difficult to work with in the lab – including genetically engineering them. So it is much more difficult, time-consuming and expensive to generate GE vertebrate lines and test them in the laboratory and then the field. However, exciting research has been conducted into developing these GE strategies in invasive fish, toads and rodents. If these technologies can be supported to the stage they are at in insects, they could provide a valuable tool against the increasing threat of invasive pests worldwide.
Another limitation for GE vertebrates is that these control strategies usually require large numbers of GE individuals to be reared before they are released in an area to overwhelm a pest population. Large or long-lived vertebrates, for example, would most likely be too expensive to rear in the laboratory in large numbers prior to their release. In this case, a new twist on these technologies termed ‘gene-drives’ could be used. In gene-drives, the genetic modification (the engineered gene) is designed to spread through the pest population once it is released, thus requiring the release of far fewer GE organisms. This could still cause population eradication in a specific area by turning every pest that inherits the gene into a male so that eventually there are no females left to mate with. These gene-drive technologies, however, are inherently less controllable than those that cause death when inherited and are therefore more controversial. New technologies are being developed to allow lethal gene-drives to be regulated so they can be better controlled in the wild.
Why haven’t we made more use of these technologies for pest control? In vertebrates we are only now getting to the stage where we can test these technologies. However, for insects appropriate GE lines have existed for some time. The primary reasons for delays in adoption are regulatory hurdles and social attitudes about genetic engineering. In order to see if these technologies are effective in the ‘real-world’ we need to test them in the wild. So far only one GE insect, the dengue fever mosquito, has been field tested. However, attitudes about GE insects are beginning to change, and this will be accelerated if current trials show that GE insects can help reduce mosquito-transmitted diseases or reduce the use of agricultural insecticides. We hope that with more testing regulatory agencies and the public can make evidence-based decisions on the use of GE technologies for controlling invasive and endemic pests in an effective and sustainable manner.
Contributions to this answer, from Tim Harvey-Samuel.
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