A pesticide that’s friendly to everything…except whitefly

We all know how crucial RNA has been in curbing the COVID-19 pandemic. But RNA has a myriad of other applications – including, perhaps, as an environmentally-friendly pesticide.

Australian researchers have developed an RNA-based pesticide that targets just one pest – whitefly – while otherwise degrading harmlessly in the environment.

The pesticide, called BioClay, could also be tweaked to target other insects, viruses, or other pathogens.

“It won’t do anything to your plant, it won’t do anything to the honey bees and the butterflies, it will just be targeting that particular pest, or virus, or fungus,” says Professor Neena Mitter, director of the Centre for Horticultural Science at the University of Queensland, and leader of the research team that developed the pesticide.

Using RNA in agriculture is not a new idea.

“The very first paper on using RNA strains to control virus infection was as early as 2003,” says Mitter.

But there’s been chemical problems holding the development back.

“RNA, on its own, is very fragile,” says Mitter. “I thought, ‘Why isn’t everyone jumping up and down? This is such a wonderful tool.’ And then when you read all those previous publications, you come to the end and it says the protection window will last only three to five days.”

BioClay’s innovation is the “clay” part: a substance that keeps the RNA stable. This clay is made from minerals referred to as “layered double hydroxides”. They’re biodegradable, and break down in nature.

“It slowly releases the RNA so that the protection can last for a little longer to make it viable for the growers.”

Mitter says that the RNA-containing BioClay can work as a type of platform technology – much like the wrapping for mRNA COVID vaccines.

“We look at the genes of the pest or pathogen we are interested in. And we figure out the gene that, if interfered with, the pathogen or pests may not be able to survive. Then we just use an RNA sequence from the pest or pathogen itself, which can interfere with that gene.”

Mitter says this is a “nature versus nature” way of dealing with pathogens.

The team has just published a paper in Nature Plants, showing the pesticide’s efficacy against whitefly (Bemisia tabaci), a sap-sucking insect which causes billions of dollars of damage to crops around the world.

“We looked at hundreds of genes of white flies: genes which may control reproductive cycles, genes made may control respiration, their mobility, different functions.

“Then we created hundreds of RNA molecules for all those genes and fed them to the white flies. Then we select: which are the ones which are causing mortality of white flies?”

Mitter says that finding these RNA sequences is a tricky process: lead author PhD student Ritesh Jain spent “countless hours counting those eggs, sitting over a microscope”.

But once they’d found the effective sequences, they had an effective method of targeting one specific pest in a very powerful way. Whiteflies which eat the BioClay sprayed onto plants will either be killed by it, or unable to reproduce.

“Multiple stages of whiteflies are affected,” says Mitter.

“If the eggs are there laid on such a plant, which has been sprayed with this RNA, they don’t hatch. The nymphs, which is the second stage of whitefly cycle, don’t grow or they are abnormal. And then of course, there is an adult whitefly mortality.”

The team is now looking to target other pests, using the same platform technology. They’ve partnered with agricultural company Nufarm to test the pesticide on farms.