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Tackling Zika: how bacteria can be a Trojan horse in fight against disease-bearing insects

Bacteria in the gut of disease-bearing insects – including the mosquito which carries the Zika virus – can be used as a Trojan horse to help control the insects’ population, new research at Swansea University has shown.

The results showed declines in fertility of up to 100% and an increase of 60% in the mortality rate of larvae, amongst the insects studied.

The findings, which are published in Proceedings of the Royal Society B, come as the World Health Organisation calls for all avenues to be explored, including research using genetic technology, in tackling the Zika virus.

The Swansea team’s findings offer the prospect of a much more targeted approach to insect control, targeting only the insect in question, and without the significant downsides of chemical pesticides, such as environmental damage, health risks, and insects becoming resistant.

The technology at the heart of the team’s work is called RNAi, a natural process that cells use to turn down, or silence, the activity of specific genes, for example the genes that control fertility.

Although RNAi has been investigated previously in relation to insects, the problem has been how to deliver it effectively. Injection into selected insects is one delivery method, but this is time-consuming and expensive, and many insects are simply too small for this to be viable.

The Swansea team’s research, which is described as “a significant advance”, demonstrates that bacteria can be an effective delivery vehicle for the RNAi.

Their technique, known as symbiont-mediated RNAi, uses friendly (symbiotic) bacteria inhabiting an insect’s gut as a Trojan horse to deliver a “switch off” command to chosen target insect genes.

The researchers tested out the technique on two insect species:

  • The Kissing bug (Rhodnius prolixus) – these long-lived blood-sucking bugs carry the parasites that cause Chagas Disease, which affects up to 8 million people in central and south America. They are known as kissing bugs as they tend to settle on people’s faces at night.

The research showed that the technique suppressed fertility in this bug by up to 100%

  • Western Flower Thrips (Frankliniella occidentalis) – this is a very invasive agricultural pest affecting many parts of the world, which has developed resistance to pesticides

The technique resulted in an increase of 60% in the larvae mortality rate of this species

In the light of these findings, the researchers conclude that: “this represents a significant advance in the ability to deliver RNAi, potentially to a large range of non-model insects.”

Symbiotic bacteria expressing green fluorescent protein from the gut of the pest insect Western flower thrip
Symbiotic bacteria, here expressing green fluorescent protein, from the gut of the pest insect Western flower thrips (Frankliniella occidentalis)
Image: Swansea University