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Sustaining Ladybug Life

May 27, 2021

How RNA can target pests like the Colorado potato beetle and save beneficial insects

We have a problem. Insect populations worldwide seem to be dying and although solid research remains scant and populations vary year to year, scientists agree that insects are at risk and the pesticides we use to keep crops healthy are probably partly responsible.

The solution, though, isn’t to simply stop the use of pesticides, a vital part of modern agriculture. So how do we eliminate intended targets without killing beneficial insects that keep our ecosystems healthy? In order to keep feeding the world, we need more sustainable ways of getting rid of pests. Products with RNA offer one pathway to pesticide replacement. By allowing the targeting of a specific organism, they may provide farmers with a revolutionary new tool. 

“There’s a ton of evidence that, broadly, insect populations in Europe and North America are declining,” says David Goulson, a professor of biology at the University of Sussex in the UK. “Some studies suggest frighteningly fast.” Professor Helen Roy, an entomologist at the UK’s Centre for Ecology and Hydrology, agrees that some species are definitely struggling. Vital to ecosystems and agriculture, insects “do amazing things in the soil, are pollinators and pest controllers,” she says. 

Defoliated potato plant field
A defoliated potato plant field as a result of the Colorado potato beetle. Traditional pesticides used to control these pests harm beneficial pollinators like ladybugs, honeybees and others.

The Intergovernmental Panel on Biodiversity and Ecosystem Services lists five main drivers of biodiversity loss: land-use change, climate change, pollution, natural resource use and exploitation, and invasive species. Pesticide use would come under pollution. Kelly Jowett of the Rothamsted Research Institute studies carabids, a species of predatory beetle that preys on several pest insects. She says that researchers often don’t ask the right questions, so lab studies might say “our pesticide doesn’t kill the carabids. [but don’t] measure them six months later to see if they’re less fecund, whether they still breed or behave properly.”   

Goulson agrees “there are examples [of studies] that stand out, especially with regard to neonicotinoids. There’s fairly clear evidence that patterns of bee decline seem to be closely linked to patterns of neonicotinoid use, and that freshwater pollution with the insecticide in the Netherlands predicts loss of water insects. In Lake Shinji in Japan, there was a massive collapse in invertebrate life, which precisely coincided with the introduction of neonicotinoids into the surrounding fields.” Since then, these pesticides have largely been banned in Europe. In this breach lies the opportunity for solutions that target pests while supporting surrounding biodiversity.  

Brian Manley, director of product biology at GreenLight, points out that pesticides can kill beneficial creatures that help crops and even cause the pest species to flare up. “An example is spider mites,” he says. “They’re a significant pest in drier conditions. Several beneficial insects feed on spider mites, and they do a great job of managing the population without the need for insecticide programs.” The use of broad-spectrum insecticides “flares the mite population, because they kill the beneficials that manage them.”

Colorado Potato Beetle on a leaf
Colorado potato beetles are major pests across North America

Another example is aphids. “Ladybird beetles eat aphids and do a good job managing them, so farmers don’t have to worry about spraying for aphids,” he says. “If you knock out the ladybug, you flare the aphid populations.”

There’s a wider problem, which is that the repeated use of any pesticide will create strains of insect resistant to that pesticide, via the same mechanism that creates microbes resistant to antibiotics.

Ron Flannagan, GreenLight’s vice president for plant health research and development, cites the weed-killer Roundup as the classic example. “It initially controlled the vast majority of weed species, but with repeated use year after year across the farm without alternating modes of action, RoundUp is now far less effective due to resistance development.”

Insecticides such as DDT and organophosphate were widely used after the Second World War and led to large jumps in crop yields, says Goulson. But they then became less effective, so farmers had to use increasing amounts to achieve the same effect. “Farmers are in a tricky position,” he says. “They’re squeezed on profitability and struggle to make a living, so they can’t afford to lose crops to pests. One factor is risk aversion: the safest thing if you’re not sure is to spray, so if there’s a chance he’ll lose the crop if he doesn’t spray, he’ll spray.”

Pests can be controlled through other means—natural enemies, crop rotation, and the gold standard of “integrated pest management,” which encourages those methods and uses pesticides only as a last resort. “According to EU law, all farms have to use it,” Goulson says, “but it’s so loosely defined that it’s barely enforced. An added challenge is that no-pesticide systems can take time before beneficials are established.  

The advantage of RNA pesticides  

GreenLight’s pesticides–based on double-stranded RNA that targets the destructive pest–can respond to some of these field and mindset challenges. A key feature of the approach is that the RNA sequences target particular processes related to a specific insect, meaning that it should have no effect on other animals. “We can design with great specificity from the outset, looking at a particular process in the target insect,” says Ken Narva, head of entomology at GreenLight. 

Mixed with water and sprayed using conventional methods over crops, the RNA enters the cells of a target pest—–specifically the Colorado potato beetle—at a rate of a few grams per hectare (equivalent to 1 teaspoon per football field). This amounts to less than one-tenth the amount of conventional industrial chemicals normally used on fields. The Colorado potato beetles eat the treated foliage and ingest the material, which selectively targets the pest and does not affect any other organisms. The liquid formulation convinces the defoliator beetle’s digestive system that it has made the protein necessary for excretion, which causes it to stop eating potato leaves and eventually expire from its own toxins. Beneficial insects—including bees, butterflies, and the closely related ladybug—are unaffected. 

How the dsRNA mixture is delivered to the Colorado Potato Beetle
How the dsRNA mixture is delivered to the Colorado Potato Beetle

Growers often face more than one pest. “In the case of a potato farm, thousands of acres might need treating on a weekly basis,” says Manley, “so cheaper and easier is what they want. The Colorado potato is the number 1 insect pest to potatoes and can affect other plants in the nightshade family–like eggplant.”

Placed in direct comparison with their traditional counterparts, RNA pesticides appear to be as effective as a market-leading rival at killing the Colorado potato beetle. “From the trials we’ve performed so far,” says Flannagan, “it’s been statistically indistinguishable from the control, in terms of foliage protection and yield protection.” It may take longer—most traditional pesticides are neurotoxins and kill their targets in a few hours, whereas the RNA solution takes a couple of days—but the crop protection appears to be comparable, according to Manley.

Untreated vs treated plots of potato plant
The success of RNA alternatives: untreated (where the pest decimated the plants to the ground) versus treated plots, where the potato plants remain.

Russ Groves is a professor and department of entomology chair at the University of Wisconsin-Madison, where field trials are being conducted. “When we started working with GreenLight and looking at the target, I was pleasantly surprised at the effectiveness of the compound compared with other biologics,” he says. “It maintains a very adequate level of protection of the commodity that to me is appropriate at large commercial scales.”

RNA has other advantages

Another advantage of RNA is its fragility. Long molecules like RNA break down more easily than the short ones used in traditional pesticides, and RNA is digested quickly, lasting only a few days when exposed to the environment. 

Because RNA is naturally occurring and is present in every living thing, “we eat RNA every day, and in most organisms, it degrades in the digestive system,” says Narva. 

Although RNA pesticides might not provide the magic bullet for plant-destroying pests, they can be a powerful tool in integrated crop management. “What we recommend is that if you have two generations of Colorado potato beetle,” says Flannagan, “you use this on the first generation and a pesticide with a different mode of action on the second in order to minimize the risk of selecting for resistant insects.”

It’s an approach that balances common sense, a judicious use of pest controls, and a respect for the environment. “Consumers are interested in thinking about supporting agriculture that is as sustainable as possible,” Groves says. “What GreenLight is working on looks like it will have a fit with the commercial industry. These new tools are the kinds of approaches that can potentially revolutionize what sustainability means.” 

Harnessing a fundamental process of a natural system without using synthetic chemistry, Groves says, holds a lot of promise. “It is part of the forefront of transforming agriculture.”