Dengue carrying mossies hit hard

The Cayman Islands Mosquito Research and Control Unit and Oxitec have cited an 80 per cent reduction in the numbers of Aedes Aegypti mosquitoes in Grand Cayman after introducing genetically modified mosquitoes into the environment as a control measure. 

This finding, which was officially published in a report in Nature Biotechnology, was previously reported in the 17 January, 2012, edition of the Caymanian Compass.  

One of the main reasons the report said led to the Cayman Islands “having a need the need for alternative measures of control” was the high level of resistance to insecticide shown by Aedes Aegypti mosquitoes in Grand Cayman. The report references research done by MRCU Entomologist Angela Harris and Hilary Ranson of the Liverpool School of Tropical Medicine, who in their findings, “Pyrethroid Resistance in Aedes Aegypti”, stated: “The Grand Cayman population of Aedes Aegypti is highly resistant to DDT and pyrethroid insecticides.” 

In an interview with the Caymanian Compass, Dr. Harris said, “For our experiments regarding the issue of resistance to insecticides we used mosquitoes that have been in a secure environment for over 30 years in a colony that was bred repeatedly over time and then compared those with the mosquitoes from the Grand Cayman. The results indicated that those found here are much more resistant and could be exposed to DDT for up to eight hours.” 

Ms Harris added that the Aedes Aegypti mosquito has only been in the Cayman Islands since 2002 and could have likely acquired its resistance from its places of origin, which have not been determined. She also surmised that their resistance level could be as a result of cross-resistance from a pyrethroid resistance. In any event, much of Dr. Harris’ research going forward will be to substantiate the theory that the mosquitoes came to the Cayman Islands with the resistance as opposed to developing it here. 

The Cayman Islands has never used DDT in its mosquito control efforts.  

However, the Mosquito Research and Control Unit of the Cayman Islands was scrutinised in the foreign press for using genetically modified Aedes Aegypti 
mosquitoes to combat the spread of dengue fever. It was the first time the method was being used in a real world test area. 

At the time, Bill Petrie, director of MRCU, said the initiative was essentially a new spin on an old technique in which males that were made sterile were released. He added that the difference here is that the male mosquitoes’ genes were altered, as opposed to their sterility being chemically induced by radiation. 

“MRCU along with Oxitec of Oxford University ran the trial for six months,” Mr. Petrie said. “We chose a small isolated area in East End. This was done in three blocks; one block was where the method was introduced, while nothing was done in another block and the third block was used to monitor the natural population of the Aedes Aegypti mosquito. 

“Once the team perfected the technique, monitoring was done by traps. The final statistical analysis has shown a significant reduction in the population of this potential dengue carrier,” he added. 

Mr. Petrie said the male Aedes Aegypti mosquito cannot bite and lives a short life-span and since their eggs will not survive using this new method of control, the population of the species has decreased, as did the probability of dengue fever transmission. 

Since the Cayman Islands’ success using the genetic modification technique, several other jurisdictions are following suit.  

“Dengue is a dangerous and debilitating disease, which affects up to 100 million people each year. The incidence of dengue has grown very rapidly in recent years: it is now a serious threat to global health, and the only means of prevention is to target the mosquitoes which carry it. We need new tools in the fight against these dangerous pests, and today’s publication shows that Oxitec’s approach can provide that,” Mr. Petrie said. 

Dengue mosquito survey

An MRCU survey officer looks for signs of dengue mosquitos during a routine inspection. – Photos: Submitted


  1. There was no public announcement before they conducted these tests. Not even did our MLA were well informed of the British company coming here to do their testings in Cayman. Yes… the test may have caused a positive result in the reduction of the Aedes Aegypti mosquito, but what about those genetically modified mosquitoes?

    Are there after effects or repercussions to these mosquitoes being in our wild?

    And what concerns me most, what precendent is this setting us up for more future tests by scientists where Caymanians could possibly be used as guinea pigs? It is a bad precedent that these things can go on without the public being properly noticed before hand.

  2. Sure, Bodden, I can see it now. As part of the newly approved budget, devious politicians begin bribing the world’s geneticists using funds generated by the hotly debated Voter Turnout Enhancement Fee. After very little research and planning, they begin introducing buff, blue-eyed Caymanian adonises to the general population. But they are not sterile my friend. Indeed, the mere sight of one of these genetically altered pieces of eye candy will have ovaries dropping eggs like the Skittles Rainbow. Initially, the ensuing population boom results in a return of the real estate market and everyone is happy. But as overpopulation grips the island, it soon becomes evident that the only solution is for the government to agree to a land and sea swap deal with Dart to extend the ETH to Little Cayman.

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