Genetically Engineered Mosquitoes Cross With Natural Species

Biotech company Oxitec has created genetically engineered (GE) mosquitoes in an attempt to control mosquito-borne diseases like yellow fever, dengue, chikungunya and Zika.

The male Aedes aegypti mosquitoes have been genetically engineered to carry a "genetic kill switch," such that when they mate with wild female mosquitoes, their offspring inherit the lethal gene and cannot survive or reproduce in the wild.

Except, the GE mosquitoes have already been released in Brazil, and researchers monitoring the project have found the GE genes have crossed with wild mosquitoes — despite the company’s assurances that this wouldn’t happen.

In a press release from Yale, senior study author Jeffrey Powell, professor of ecology and evolutionary biology, noted, “The claim was that genes from the release strain would not get into the general population because offspring would die … That obviously was not what happened.”1

GE Mosquitoes Passed Genes to Native Mosquitoes

The largest release of Oxitec’s GE mosquitoes, dubbed OX513A, occurred in the city of Jacobina in Bahia, Brazil. About 450,000 male mosquitoes were released weekly for 27 months in the region in an attempt to reduce numbers of disease-carrying mosquitoes.2 “If lethality is complete, releasing this strain should only reduce population size and not affect the genetics of the target populations,” researchers wrote in Scientific Reports.3

However, this wasn’t the case. The researchers monitored the population of Ae. Aegypti mosquitoes in Jacobina to determine if the release of GE mosquitoes was affecting the genetics of the wild population by transferring genes. The GE mosquitoes contain a fluorescent protein gene, which allows the GE offspring to be detected.

When analyzed six, 12 and 27 to 30 months after release, the researchers found “clear evidence that portions of the transgenic strain genome have been incorporated into the target population.”4 The study explained:5

“Evidently, rare viable hybrid offspring between the release strain and the Jacobina population are sufficiently robust to be able to reproduce in nature. The release strain was developed using a strain originally from Cuba, then outcrossed to a Mexican population.

Thus, Jacobina Ae. aegypti are now a mix of three populations. It is unclear how this may affect disease transmission or affect other efforts to control these dangerous vectors.”

This shouldn’t come entirely as a surprise, since in lab tests up to 4% of OX513A offspring, which were the result of matings between OX513A and wild type mosquitoes, did survive into adulthood.6 However, on their website, Oxitec used to state, “After an Oxitec mosquito has successfully mated with a wild female, any offspring that result will not survive to adulthood … ”7

That page has since been taken down, but the company is still touting the “self-limiting gene” that’s supposed to “disappear from the environment”:8

“Our insects contain a self-limiting gene, and when this gene is passed on to their offspring, offspring do not survive to adulthood, resulting in a reduction in the pest insect population. We call this method “self-limiting” because the released insects and the self-limiting gene that they pass on are designed to die and disappear from the environment.

We release males, because it is the female insects that are directly responsible for spreading disease or producing larvae that damage crops. Our males have one job: to find wild females where they live and mate with them … The self-limiting gene prevents offspring of our released male insect from surviving to adulthood … ”

Mosquito Population Rebounds After Initial Decline

Oxitec has stated that releasing their OX513A mosquitoes may reduce local mosquito populations by 90+%.9,10 It sounds impressive, but the featured study revealed that, after an initial decline, the mosquito population rebounded about 18 months after the GE mosquitoes were released.

Powell suggested the rebound may have occurred because female mosquitoes started to avoid mating with the GE males, a phenomenon that’s also occurred in tests when sterile male mosquitoes were released. What’s more, the “tri-hybrid population” that’s now been created from the Cuba, Mexican and Brazilian lines are “genetically distinct” and may be even heartier than previous mosquitoes:11

“The three populations forming the tri-hybrid population now in Jacobina (Cuba/Mexico/Brazil) are genetically quite distinct, very likely resulting in a more robust population than the pre-release population due to hybrid vigor.”

Depending on the sample tested, anywhere from 10% to 60% of the mosquitoes in the area were found to contain some OX513A genome.12 As for what this may mean for the future, no one knows. Powell stated:13

“ … [I]t is the unanticipated outcome that is concerning … Based largely on laboratory studies, one can predict what the likely outcome of the release of transgenic mosquitoes will be, but genetic studies of the sort we did should be done during and after such releases to determine if something different from the predicted occurred.”

Oxitec Wants to Release GE Mosquitoes in Key West

Oxitec has been trying for years to get approval to release its controversial GE mosquitoes in the U.S., specifically in Key West, Florida. They’re no longer pursuing a plan to release OX513A mosquitoes, but instead have turned their efforts to second generation “Friendly” mosquitoes. These GE mosquitoes carry a self-limiting gene that prevents female offspring from surviving, allowing only males to be produced. Oxitec explained:14

“After releases of Friendly™ males into the field, which find and mate with wild female mosquitoes, reduction of the target population is achieved as the female offspring of these encounters cannot survive.

Male progeny survive, carrying a copy of the self-limiting gene; in turn, these males are able to pass on the self-limiting gene to half of their offspring, of which female carriers of the gene cannot survive.

The self-limiting gene can thereby persist but declines over time, offering potentially multiple but still self-limiting generations of suppression for every Oxitec FriendlyAedes aegypti male released.”

The second-generation GE mosquitoes have already been tested in Brazil, with additional field trials planned there in 2019 and 2020. In the U.S., the EPA has accepted Oxitec’s application to bring the GE mosquitoes to Key West, and a 30-day public comment period, which ends October 11, 2019, is underway.

The finding that Oxitec’s OX513A mosquitoes have spread their GE genes to local mosquitoes has opponents concerned. Barry Wray, executive director of the Florida Keys Environmental Coalition, said the coalition intends to try to extend the public comment period and told WUSF News:15

"It's another verification of the unquantified risk associated with these genetically modified mosquitoes … A new version based on the same lethal gene technology represents the same problems, with just a new marketing discussion wrapped around it."

Tinkering with genes often results in unexpected consequences, and the researchers of the featured study suggested that the transfer of genetic information may even introduce other genes, such as insecticide resistance.16

Already, research published in the journal Oecologia has shown that mosquitoes are developing resistance to commonly used agricultural insecticides, but their predators are not, creating the perfect environment for mosquitoes to flourish.17 More caution is warranted in the case of GE mosquitoes, which have now become largely out of control in the environment, notes Christoph Then for Testbiotech:18

“The Oxitec trials have led to a situation that is largely out of control. The company has released its patented insects although it was known before that some insects could survive in the environment. The expectations of their investors was more important than the protection of health and the environment.

There is no insurance and no fast-track mechanism to prevent severe damage in a worst-case scenario. This incident must have consequences for further applications of genetic engineering. Preventing the spread of genetically engineered organisms within natural populations has to become a priority.”

Wolbachia Mosquitoes Released in Miami

In January 2018, lab-bred Aedes aegypti mosquitoes carrying wolbachia bacteria were released in South Miami, Florida. It was the first phase of the Miami-Dade County Mosquito Reduction Test Program, which targeted a one-half square-mile treatment area that received the altered mosquitoes and a corresponding control area within the city.

The project was conducted by the Miami-Dade County Mosquito Control & Habitat Management Division in collaboration with MosquitoMate, Inc., which created the technology. MosquitoMate’s lab-bred male mosquitoes are infected with wolbachia bacteria, which is naturally occurring in up to 60% of insect species, but not in Aedes aegypti mosquitoes.

When the male wolbachia mosquitoes mate with female mosquitoes in the wild (which do not carry the bacteria), the resulting eggs do not hatch, which means the number of Aedes aegypti mosquitoes in the area should ultimately decrease.19

In Miami-Dade County, the MosquitoMate trial was said to result in a 75% reduction in mosquitoes due to egg hatch failure.20 Tests using the so-called “biological mosquito technology” are also underway or completed in the Florida Keys; Clovis, California; St. Augustine, Florida; and Harris County, Texas.21

One of the problems with wolbachia mosquitoes is that the bacteria can spread to local mosquitoes, with unknown consequences, and once the insects are released, there’s no going back.

Further, it’s not a permanent solution but one that must be reapplied, as the mosquito population will rebound, necessitating the release of more MosquitoMate mosquitoes.22 There’s also the potential ramifications to the ecosystem, which can occur whenever any species is removed or drastically reduced.

While mosquitoes are primarily viewed as a nuisance and vector for deadly diseases like malaria, there may be downsides to eradicating them entirely, such as removing a food source for other creatures.

Natural Options for Mosquito Control

More than half the people on Earth live in an area where disease-carrying mosquitoes are present and, every year, mosquitoes cause millions of deaths from diseases like malaria, dengue and yellow fever.23 So, there’s no question that mosquito control is important.

Mosquitoes breed in standing water, including that found in pet bowls, gutters, garbage and recycling bins, spare tires, bird baths and children’s toys. Draining these water sources can help eliminate mosquitoes from your yard.

To avoid getting bitten, wear long sleeves and pants in mosquito-prone areas and use natural insect repellants (not synthetic chemical versions), like cinnamon leaf oil, citronella essential oil or catnip oil, as necessary.

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