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Using their genes against them: fighting insect pests with genetic targeting

Using their genes against them: Fighting insect pests with genetic targeting - 7 January 2013. Saskia Hogenhout, JIC
News from: John Innes Centre

When you look out on a golden-yellow field of oilseed rape you might not think you're seeing a battleground, but crops including oilseed rape, wheat, potato and tomato are engaged in a constant fight with pests and disease, trying to stay one step ahead.

As the world's human population looks set to increase to nine billion people by 2050, keeping plants healthy and productive is going to be essential to making sure there is enough food to go round.

"Crop pests are emerging earlier due to global warming and new variants are arriving from other countries, bringing new plant viruses", said Dr Saskia Hogenhout from the John Innes Centre (JIC) in Norwich, an institute strategically funded by the BBSRC.

Among these pests whitefly and green peach aphids cause hundreds of millions of pounds of damage and loss to crops through transmitting viruses and feeding. Both species are notorious for demonstrating the ability to rapidly develop resistance to conventional pesticides, and both attack a wide variety of crops, including cabbage, lettuce, beet, oilseed rape and potato.

In UK cereal crops aphids alone can cause yield losses of over 40 per cent, and insect pests are responsible for an estimated 15 per cent of all crop losses globally.

Dr Hogenhout said: "The aphids and whitefly themselves are problematic but they also transmit more than half of all plant viruses.

"They're called the mosquitoes of plants because like mosquitoes they feed on the vascular system and they transmit quite a number of viruses.

"The green peach aphid has the world record of all insects for resistance against pesticides, it has developed resistance to 71 different chemical compounds on the market, compared to the diamondback moth, Plutella xylostella L., which has the second score with 51.

"We really need to work hard to make sure this insect is controlled."

Last year Dr Hogenhout received a Bill and Melinda Gates Grand Challenges Explorations grant to grant to work with Dr Eduardo Bejarano from the University of Malaga and Dr Ian Bedford of the JIC Entomology Facility, to tackle the problem of whitefly and whitefly-transmitted viruses of cassava in Africa.

Dr Hogenhout and her colleagues at the JIC hope that examining the genetic code of closely-related pests, including whitefly and green peach aphids, will lead to new ways to control them. They are working with The Genome Analysis Centre (TGAC), Rothamsted Research and the University of Greenwich, as well as research teams based in France and USA.

An understanding of the DNA of pests could be used to develop targeted pesticides or genetically modified plants that are able to silence genes essential for the pests' interactions with crops. Targeting these genetic "Achilles' Heels" could be used to prevent aphid and whitefly feeding on crops and to stop the transmission of viruses without affecting other species, including the people who will eventually eat the crop.

So far Dr Hogenhout's research has worked on developing a technique called plant-mediated RNAi. This genetic modification technique allows plants to produce molecules that prevent an insect from properly expressing certain genes.

It does this by manufacturing 'interfering' ribonucleic acid (RNAi), which targets a molecule called messenger RNA, crucial for a gene to be properly decoded. The RNAi degrades messenger RNA, stopping the insect's genes from being translated into proteins and so 'silencing' it.

Dr Hogenhout said: "Whitefly and aphids are sister species, quite closely related, and by comparing their genomes we may be able to find some groups of genes that are specific to them, and those might be able to be targeted with plant-mediated RNAi.

"We are already working with companies to see how we can use the information for controlling these insects, either by genetically modifying plants or by classical breeding."

Dr Hogenhout believes that things are looking promising.

"We're making good progress," she said. "Right now we're at the stage of developing techniques like plant-mediated RNAi and silencing technologies, and also the sequencing stage, so we are in the process of discovering things. I'm very optimistic about it."

Whatever the outcome of the research, the knowledge gained about these important and persistent pests is likely to be valuable in the continuing battle against these hardy and continually evolving creatures.

As Dr Hogenhout says: "You need to know your enemy."