(Beyond Pesticides, November 29, 2018) The British Cayman Islands will no longer fund the release of genetically engineered (GE) mosquitoes, as reports indicate that the program failed to achieve its intended goals. The government is formally terminating its contract with the UK-based company Oxitec, which marketed GE mosquitoes as a sort of silver bullet for the management of diseases such as Zika, yellow fever, malaria, and dengue. Advocates opposed to the GE mosquito program are continuing to encourage a focus on education and source reduction as the best method to address mosquito-borne diseases.

Oxitec first began introducing its line of GE mosquitoes earlier in the decade, at a variety of locations including India, Brazil, Malaysia, and the Florida Keys. Public opposition to the release has been consistently strong. In the Florida Keys, over 230,000 people signed a change.org petition opposing the release. In the Cayman Islands, residents launched a number of lawsuits. In each instance the company was granted free reign to initiate its program.

GE mosquitoes aim to ‘gene drive’ mosquito populations out of existence, a process intended to propagate a particular set of genes in a species. The company developed GE mosquitoes in a laboratory, injecting a gene that produces sterile male mosquitoes. Male GE mosquitoes are then released into the environment en masse, in the expectation that they will outcompete other male mosquitoes and breed with available females. Females that mate with the male GE mosquitoes are expected to produce offspring that die before they hatch.

British-based environmental group Genewatch UK has consistently opposed the release of GE mosquitoes, arguing that there were a number of risks associated with this work. One concern is that the mosquitoes rely on the antibiotic tetracycline to act as a chemical switch, allowing the GE larvae to develop under lab conditions. Thus, low levels of tetracycline in the environment could undermine effectiveness, and result in only short-term mosquito population reductions. In addition to efficacy, many note public health concerns relating to the introductions of novel genes into the environment.

This is how the mechanism of the GE mosquito is supposed to work, according to the article Genetically engineered mosquitoes, Zika and other arboviruses, community engagement, costs, and patents: Ethical issues, published in PLOS:

“The GE mosquito: How does it work?

The GE OX513A Aedes aegypti has been subject to a germline modification that includes a lethality gene. Specifically, a synthetic genetic sequence encoding a tetracycline-repressible transcriptional activator (tTAV) is introduced into the mosquito with the intent of creating tetracycline dependency in the insect. In the absence of tetracycline, tTAV is expressed, and this leads to the death of most of the mosquitoes carrying the trait [4]. If tetracycline is present (as it is during the mosquito rearing in the laboratory, for example), then tTAV is repressed and the larvae can develop and reach adulthood. Female mosquitoes are the biters that spread the disease, so only the male GE mosquitoes are intended for release in the target area.”

The Cayman Islands government had contracted with Oxitec for the last two years. In May, a $720,000 deal was renewed, but Oxitec said at the time that it would be integrating other management techniques alongside the release of GE mosquitoes. However, ultimately, as the territory’s environmental health minister told the press, “The scheme wasn’t getting the results we were looking for.” Cayman Island’s Mosquito Research and Control Unit (MRCU) appeared to reflect the same concerns as advocates in explaining its reasoning, citing concerns over the spread of antibiotic resistant bacteria, and risk of lowered immunity to mosquito-borne diseases.

Based on the results seen on the ground, GE mosquitoes are likely not worth trading one public health risk for another. Scientists continue to look into more natural alternatives to genetic modification, focusing on the use of a bacterium called Wolbachia, which would function in a similar manner to Oxitec’s mosquitoes. Wolbachia-infected male mosquitoes mate with females who would then be unable to produce offspring. However, like GE mosquitoes, the efficacy and safety profile of this approach is also lacking.

An arsenal of highly toxic adulticides that include organophosphates like naled, chlorpyrifos, malathion, and pyrethroids like permethrin and sumithrin are often the first line of treatment for mosquitoes in many communities. These pesticides have been linked to a host of adverse effects, including neurotoxicity, cancer, and reproductive dysfunction. Further, adulticiding has been shown to be the least effective method for reducing mosquito populations, as these chemcials are indiscriminate and just as likely to harm non-target insects as they are mosquitoes.

Management of disease-carrying mosquitoes can be successful when emphasis is placed on public education and preventive strategies. Individuals can take action by eliminating standing water, introducing mosquito-eating fish, encouraging predators, such as bats, birds, dragonflies and frogs, and using least-toxic larvacides like bacillus thuringiensis israelensis (Bti). Community-based programs should encourage residents to employ these effective techniques, focus on eliminating breeding sites on public lands, and promote monitoring and action levels in order to determine what, where, and when control measures might be needed. Through education of proper cultural controls, and least-toxic and cost effective biological alternatives, the use of risky technologies such as toxic pesticides and GE mosquitoes can be avoided.

For more information, see Beyond Pesticides’ mosquito management program page and comprehensive Public Health Mosquito Management Strategy.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: Edmonton Journal