USDA Approves Release Of Genetically Modified Moth

You may remember last year when the USDA approved a field trial of genetically modified mosquitos in Florida. Although there were the usual ideologically opposed protests the trial is progressing. Well, last week the USDA approved another field trial of a GM insect, this time the diamondback moth.

The diamondback moth is an invasive species to the US and causes millions of dollars of damage to cabbage, broccoli and other brassicas every year. Now, I know what you’re thinking: “cabbage is gross, I wouldn’t care if the whole crop was lost.” I understand, I’m with you, but the cabbage farmers would be upset so we’ve got to do what we can.

In this instance, that means releasing male GM moths into the environment. When these moths breed with a female one of two things will happen. Either female offspring will be produced but these will not be able to survive to adulthood, or a male will be produced. In either case, no eggs are being laid, which means no caterpillars, which means no cabbages being munched away, which means no crying farmers.

The technology used is very similar to that used in the transgenic mosquitos, indeed, the modified moth is made by the same company, Oxitec, based in Oxford, UK. At its most simple level, a gene is a unit of DNA that encodes a protein. Genes contain exons, which are the coding bits that go on to make up the protein, and introns, which are gaps of non-coding sequence which break up the exons. Introns may seem like useless breaks in the gene but they allow important regulatory functions to take place.

For example, a gene might be made up of, let’s say, 20 exons. But there can be different versions of that gene that are made of the same basic components but might not use exon 19, say, in certain conditions, or maybe the first 3 exons could be dropped under other conditions. These different versions of the same gene are called transcripts and the process is named alternate splicing. You may recall the story of the world’s leading geneticists trying to predict the number of genes a human would have before the first draft of the human genome was published. The clever money was in the 50,000-120,000 gene ball park. The winner was a lady who just guessed the lowest number and even she was a few thousand too high.

We actually have in the region of 22,000 genes, about half the number a rice plant has. What those early genetic pioneers didn’t realise was how many different transcripts would be present for each gene. In humans, we average nine different transcripts for each gene and, just like that, we all of a sudden have an order of magnitude more complexity to our genomes.

Back to the diamondback moth. Researchers noticed that there are certain genes in the moth that are alternately spliced dependent upon whether they are inside a male or a female. Identifying this ready made sex-dependent difference within the species gave them a target for the introduction of a DNA sequence that would selectively kill female offspring.

With the release of tens of thousands of these transgenic male moths into the environment would result in fewer females being produced, fewer eggs being laid and fewer caterpillars.

Unlike using a pesticide this is a completely toxin-free solution to curbing this population. Also, as the male moths will only mate with females of the same species, it is extremely specific to the population in question meaning fewer off target effects. This is a big plus for the environment.

No doubt the project will have it’s detractors, but so long as they keep bringing ideals to an evidence fight I see no reason to pay them any heed here. When the trial will take place is currently unknown and will dependent upon the glacial manoeuvrings of the USDA. Progress, though, continues.

The diamondback moth, Plutella xylostella. Image courtesy of Olaf Leillinger.

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