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, according to an article in the Proceedings of the Royal Society B.
The technology at the heart of the researcher’s work is called RNA interference (RNAi), a natural process that cells use to turn down, or silence, the activity of specific genes, for example the genes that control fertility.
RNAi has been investigated previously in relation to insects, but it is difficult 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.
Instead, scientists from Swansea University have demonstrated 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 to deliver a “switch off” command to chosen target insect genes.
The results showed declines in fertility of up to 100% and an increase of 60% in the mortality rate of larvae among the insects studied.
This is a much more targeted approach to insect control, targeting only the insect in question, and without the significant downsides of chemical pesticides.
The researchers tested the technique on two insect species, the kissing bug (Rhodnius prolixus) and the western flower thrips (Frankliniella occidentalis). The research showed that the technique suppressed fertility in the kissing bug by up to 100 percent, and the technique resulted in an increase of 60 percent in the larvae mortality rate of western flower thrips.
“This represents a significant advance in the ability to deliver RNAi, potentially to a large range of non-model insects,” the authors wrote.
Significantly, they report that the technique would be transferable to many insect species, including Aedes mosquitoes, which carry the Zika virus.
“It is expected that symbiont-mediated RNAi would be effective in other insect species,” they wrote. “The unifying prerequisite is that the insects harbor culturable symbionts, a criterion already known to be met by many globally important insect species such as Aedes and Anopheles mosquitoes, tsetse flies, white fly, and honey bees.”
The method involves identifying an appropriate bacterium in each insect to deliver the RNAi. The bacteria are specific to that particular insect and cannot live outside it.
“This technology allows us to target insects much more effectively than conventional pesticides, and without their side-effects,” said Dr. Paul Dyson, one of the co-authors. “Using bacteria as a Trojan horse gets around some of the problems in delivering RNAi to the insect. It is a significant advance. It can help us to tackle some of the insects and crop pests that have such a devastating impact on human health and the food chain. Our method could also help in the fight against the Zika virus, as the Aedes mosquito that bears the virus has bacteria that would be suitable.”
“The symbiotic bacteria basically do all the hard work for us,” said Dr. Miranda Whitten, another co-author. “They are programmed to manufacture the RNAi molecules inside the insect’s body, for as long as needed, and they do this without being detected by the insect’s immune system. As we can choose which gene — or combination of genes — to target, we now have a highly flexible gene-suppression toolbox. This is combined with an exquisite specificity that shouldn’t affect other insect species, even if they share the same habitat.”
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