In a recent blog, I congratulated Oxitec on the first release of transgenic Aedes aegypti for control purposes on Grand Cayman (GC) in the Caribbean. At that time, the results had not been made public. Today (4-Nov-2010), further information was released at the American Society of Tropical Medicine & Hygiene meeting in Atlanta, USA. Well, were those transgenic males up to the task?
Oxitec’s Director of Research, Luke Alphey, presented a summary of the results to date from their releases of OX513A strain males on GC during 2010. Males of this strain confer a lethal phenotype to their male and female progeny. (Since this is blog is a forum for me to express personal opinions, I’d like to suggest that Oxitec consider naming their strains something more friendly that conveys some phenotype information!)
First a bit of background is in order. If such technologies are ever implemented more widely, it is anticipated that male releases will be complemented with conventional control methods. The intent of this combination strategy is to pair conventional control measures that are effective at high population densities with sterile male methods which will be most efficient at low population densities.
According to information presented, population suppression of approximately 60% (my guess) was accomplished over an area of 15 hectares by releasing 5,000 males per week per hectare during the mid- to late aegypti season. The fact that the RIDL releases were not complemented by conventional methods makes the outcome even more remarkable and confirms that the males were sufficiently competitive to suppress natural target populations. Need more? Making the outcome yet more remarkable is the fact that the site was not sufficiently isolated to prevent immigration! Overall, a very satisfying demonstration.
Disappointingly for those anticipating new material for B-grade science-fiction movies and hoping for reasons to oppose any release of GMOs, no giant glowing mosquitoes have been sighted. However, the Grand Cayman Mosquito Control and Research Unit (MRCU) will continue post-release monitoring. For the time being though, those who inhabit the release area (and who were supportive of the effort) must welcome the reduced population of biting females.
Numerous predictions of failure due to poor transgenic male fitness, negative density dependence and reproduction rates have, to a limited degree, been answered by these results. The willingness of GC MCRU to conduct this trial was a courageous - but by no means risky – effort.
One good experiment is better than many speculative arguments. One can only hope that future trials will provide similar exciting results.