Genetically modified mosquitoes

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The so-called yellow fever mosquito, Aedes aegypti, is capable of transmitting yellow fever, dengue, chikungunya, West Nile virus, eastern equine encephalitis, and Zika. Of late, public health officials are particularly concerned about Zika, because if it contracted by pregnant women, their offspring are likely to suffer from microcephaly, which is characterized by their babies having abnormally small heads and brains. Zika outbreaks have occurred in Brazil, and the disease is endemic in Mexico and several places in the Caribbean region. Pregnant women are being advised to avoid traveling to the endemic areas. In addition to being bitten by infected mosquitoes and contracting Zika, the disease can also be transmitted by kissing or by having sexual intercourse with infected partners. So far, only one case of Zika has been reported in Alabama, this in a woman who had recently visited an endemic area.
Recently a British company, Oxitec, has developed a technique to reduce the populations of A. aegypti that involves genetically modifying males of the species. These modified males are released and mate with wild females. The resulting offspring are sterile. Unlike males that have been sterilized by irradiation, the “GMO males” are readily accepted by the females. Daniel Engler, in an article written in “Slate.com” and reported in “The Week,” stated that in a test in Brazil where the modified males of A. aegypti males were released, the population was reduced by 90 percent.
A proposal by Oxitec to conduct a test of modified mosquitoes in the Florida Keys has been opposed by some residents, presumably because they think it might adversely affect the food chain or the natural ecosystems. Reportedly, knowledgable scientists contend that eliminating A. aegypti or reducing the species’ numbers would have little or no ecological effects. One advocate of the proposed test said, “Some people are against GMO anything.”
Another mosquito capable of transmitting the aforementioned diseases is the alien invader, the Asian tiger mosquito, Aedes albopictus. Both of these vectors occur in Alabama, and both are also capable of transmitting heart worms in dogs and cats, as are 68 other mosquito species.
It is unlikely that Oxitec’s genetically modifying technique is capable of eradicating A. aegypti throughout its wide range. However, in one relatively small area, it was virtually eradicated during the early 1900s as a result of an ambitious undertaking by Dr. William Gorgas, using screening, pouring oil on potential breeding sites, and educating the public to eliminate potential sites on and about their premises.
His campaign allowed successful construction of the Panama Canal. Earlier, the French had attempted to construct the canal, but abandoned the effort because so many of their workers succumbed to yellow fever.
The most successful insect eradication program in history was eliminating New World screwworms from the United States. Screwworms were a serious problem for livestock farmers, especially in the southern states. Female screwworm flies would lay their eggs on any wound, and upon hatching the larvae would bore into the host and feed on its tissue. The eradication program involved releasing mechanically sterilized male flies, using irradiation, and releasing them in southern Florida, where the flies were overwintering. The sterile males would mate with females and her eggs would be infertile. The program began in 1958, and eradication of the Florida population ended successfully in 1959. Efforts continued in the remainder of the U.S. range and the population was completely eradicated in 1966. Mexico began an eradication program in 1972, and Mexico declared its effort to be a success in 1991.
Because several countries in tropical America continue to have screwworm populations, strict laws requiring animal inspection and reports of suspected infestations are rigidly enforced.
Bob Mount is a Professor Emeritus with the Department of Zoology and Entomology at Auburn University. He is also chairman of the Opelika Order of Geezers, well-known local think tank and political clearing house. He writes about birds, snakes, turtles, bugs and assorted conservation topics.

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