To Speculate On Why Oxitec’s GM Mosquitos Don’t Work

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It appears that the attempt to introduce GM mosquitoes into the wild in order to outcompete the natural ones doesn’t work. Which gives us the lovely opportunity to speculate as to why this might be. Our speculation here being that evolution doesn’t quite work that way which is going to be something of a blow to all other similar attempts. Do note, and this is important, that this is simply speculation and alarmingly ill-informed such at that. Which is, of course, what makes it all so fun:

Plans to use genetically modified mosquitoes to rid the world of diseases such as malaria, dengue, yellow fever and zika have faltered after officials admitted that a major pilot had not worked.

The British company Oxitec, which was originally a spin-off from Oxford University, engineered a line of insects whose offspring were unable to grow into adulthood, causing the population to crash.

Millions of the mosquitoes were released at the British Overseas Territory of Grand Cayman over the past two years but last week the Environmental Health Minister Dwayne Seymour admitted ‘the scheme wasn’t getting the results we were looking for’ and would not be continued.

Well, that’s not good news as we really would like to be able to control mosquito populations without spraying DDT all over the countryside. This is not exactly new news:

Documents and correspondence released to GeneWatch, a UK-based NGO, under a freedom of information request appear to show that there is no evidence that the controversial release of genetically modified Aedes aegypti mosquitoes in West Bay by Oxitec in co-ordination with the Cayman Islands Mosquito Research and Control Unit (MRCU) made any impact on the targeted pests.

A pity as we’d like something to work:

GeneWatch UK today published a new briefing on Oxitec’s GM mosquitoes(1), which have been released in open air experiments in the Cayman Islands, Panama, and Brazil. The briefing includes new evidence recently released as a result of Freedom of Information requests, which shows that scientists at the Mosquito Control and Research Unit (MRCU) in the Cayman Islands who have access to the experimental data believe there has been “no significant reduction in the abundance of Aedes aegypti in the release area”.

The briefing also highlights that, in the Cayman Islands, there was a significant increase in the number of female mosquitoes collected in the experimental release area, which is likely due to the inadvertent release of large numbers of female GM mosquitoes, which can bite and transmit disease.

Hmm, no, not quite what we want. And it all started out with higher hopes:

Dengue fever, borne by mosquitoes, kills around 20,000 people a year. Oxford-based scientists think they can solve the problem by disrupting breeding in high-risk areas with genetically modified insects. But is that safe?

And now on to the fun part, the speculation.

So, release mozzies that can’t breed – because they’re sterile, say. Or here, because juveniles don’t mature. This will disrupt the breeding cycle and lead to fewer of them around. Seems reasonable enough.

Except, except, this will only be true if the limitation upon the number is that breeding cycle. Which doesn’t have to be true.

Think about cows. One bull can cover many cows. Having two bulls doesn’t increase the number of calves born each year. Calves are 50% male, 50% female, the limitation on how many calves there will be in the next generation being, largely enough, how many female calves grow up to then breed. If one of the bullocks gets killed and eaten – by humans, wolves or bacteria – this isn’t going to affect the number of cows a generation down other than by that number of one dead bullock.

So, what’s the limitation on a mozzie population? Hmm, we dunno either. But it would appear that it’s not the number of fertile ones in the population. This is possible, obviously enough. If each fertile one has many hundreds of offspring then it’s something else which limits population. How many get eaten, or swatted, maybe. Or the supply of food. If this is so then what happens when you introduce infertile ones? Infertile in the proper sense, unable to produce offspring which then produce offspring? Well, as seem to have happened here, those which can quickly produce enough offspring to fill the ecological niche and our introduction of the infertile hasn’t made much difference.

Again, all speculation. But if this is true then the varied plans to deal with insect populations through introducing infertile variants aren’t going to work. The implication thus being not that this particular trial failed but that all such will.

Back to DDT it is then, eh?

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