Genetically modified killer moths set free


You will have heard of GM crops: plants capable of dealing with drought, floods and heat waves. The new ‘it’ word in the world of science this decade has been heralded as GM insects. Already the British Biotech company, Oxitech, working in conjunction with the World Health Organisation has attempted to reduce mosquito spread diseases such as malaria, dengue and the zika virus by introducing genetically modified mosquitos into a range of countries including Brazil and India.

These GM mosquitos are all male, and within their genetic coding hides a lethal gene which codes for death in any daughter mosquito. This ensures that half of the next generation is killed off, with the male offspring passing on the gene until the gene wipes itself out. Whilst this method of disease control seems futuristic and improbable, it has already been used in cities in Brazil with seemingly positive results.

Oxitech now has its eyes set on an even larger project, which if solved would remove a $5 billlion per year cost in damage to crops. The enemy? The diamond backed moth. Plutella xylostella, of the family Plutellidae, is a crop pest which targets plants in the Brassicacae family such as cabbage and kale.

The moths wipe out billions of dollars of potential income for farmers

The moth recognises chemicals called glucosinolates which are released by Brassica vegetables and open leaf plants; these chemicals stimulate oviposition in the moths. Once the eggs are laid, the larvae hatch and eat the majority of the plant and can destroy entire crops in a short period of time, destroying billions of dollars of potential income for both the US and China.

The diamond backed moth evolves resistance to pesticides extremely rapidly and this has caused major issues for farmers around the world. As well as resistance to general pesticides, the diamond backed moth also developed a tolerance to the Bt toxin, Bacillus thuringiensis, which targets infestations of moths, from a spontaneous mutation of an autosomal recessive gene.

Oxitech proposes releasing a batch of male P. xylostella into the wild which have an extra two genes added in. One gene only activates in females and so can be passed into native populations; it makes the moth susceptible to pesticides and will kill it. The second gene codes for a red fluorescent protein which enables scientists to track the spread of the gene through the generations.

There may be a range of unexpected secondary ecological impacts

Just like the mosquitos, the gene will have a short lifespan and as it is negatively selected for – most likely it will disappear within a few generations meaning more moths will have to be released. Although the concept of crop protection in the form of GM insects seems ingenious, there are many ecological impacts which have seemingly not been thought through.

There has also been a significant amount of research done into alternate ways of controlling the moths, without releasing mutant insects into the environment that could potentially cause a cascade of other issues. Many farmers use crop rotation, and plant other vegetables in order to disrupt the natural egg-laying seasons of the moths. Wintercress too has been used as a deterrent, as it releases similar chemicals that encourage egg laying but do not provide the necessary sustenance for the hatched larvae.

Some small-scale farmers even introduced higher numbers of the moth’s natural predators, such as lacewings, Chrysoperla carnea, in order to keep the numbers of moths under control. Although the methods of controlling the diamond backed moth population are numerous and all seemingly contentious, the cause of the spread of this moth is certain: climate change. Increasing global temperatures have allowed the crop pest to spread far beyond its native range, creating problems for more and more farmers and harming both local and global economies. Which pest is next?

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