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Genetic Sprays Use RNA Interference to Combat Pests

Monsanto is developing sprays to control weeds and insect pests by temporarily altering their genetics through RNA interference as an alternative to developing new GM crops, and could also be used to introduce traits like drought resistance.

“The single biggest problem with conventional insecticides is their effects on non-target organisms. Using RNA interference (RNAi) to kill pests through sprays of double-stranded RNA (dsRNA) has the potential to be species-specific. This individual targeting can be achieved because genes vary enough between different species that specific dsRNA could only affect the desired pest.

“However, targeting single species is not guaranteed. For example, in a recent paper we showed that a spray of dsRNA from a house fly could kill Colorado potato beetles.

“In some cases, conventional insecticides are used because they kill multiple insect pests. Thus, an insecticide that targets only one species has lots of benefits, but might not be cost-effective.

“Then there is the issue that insects always find a way to evolve resistance, and harnessing RNAi will be no different. The relative speed with which resistance will happen is a wide-open question.

“Currently, using dsRNA sprays is limited to insects that eat the leaf. Insects like aphids that consume fluids from the leaf seem much less affected. Some species are just refractory to this technology and this includes several economically important Lepidoptera (caterpillars). There may be ways to use this technology against aphids and other refractory species, but we are only in the early stages.

“There is a big gap from discovery to field application, and cost is often a big factor. Monsanto is reputed to be in the third year of field trials with their product, so they must think it has big potential, but I am not sure how Monsanto will protect their intellectual property. There are some interesting issues associated with the technology because as far as I know the gene can’t be patented.”

Dr Jeffrey Scott, Professor, Department of Entomology, Cornell University


“This is a great article because the author brings together a lot of disparate and new information to make a compelling argument. RNAi sprays are so new and proprietary that most academic ecologists like me know very little about them. It may take a while before biotech companies figure out which RNAi sprays are going to work well enough to be commercially viable, but the field is moving quickly.

“Like GMOs, these genetic sprays will need to be evaluated for health and environmental effects on a case-by-case basis. It doesn’t make sense to group them together and conclude that all of them are either safe or risky. Nonetheless, it’s important to have public discussions about safety to learn more about the scale, dosage, biological effects and persistence of new products that are in the R&D pipeline, like Monsanto’s Biodirect RNAi sprays.

“As noted in the article, the Environmental Protection Agency’s expert panel didn’t express concerns about effects of the sprays on human health, but they lacked enough information to evaluate the potential for unwanted environmental effects, including harm to non-target insects. This information gap will need to be addressed.

“In comparison to plants with genetically engineered traits, which are passed on to their descendants, the use of RNAi sprays would avoid concerns about the long-term persistence of unwanted synthetic genes in breeding lines, organic food, exported agricultural products, and related plant species that can cross-pollinate with transgenic crops. It is impossible to completely control the movement of transgenic seeds and pollen in most agricultural systems. In contrast, if environmental problems should arise with genetic sprays, their use could be discontinued.

“From this standpoint, RNAi sprays would be an improvement over the use of genome editing and other types of genetic engineering that alter an organism’s genes and cannot be contained after commercialisation.”

Dr Allison Snow, Professor of Evolution, Ecology and Organismal Biology, Ohio State University


“A problem is that there does not seem to be much specific information available about the RNA molecules being used. I’m sure Monsanto doesn’t want to reveal proprietary information until it is required to do so in order to register a pesticide, but I’d be loathe to speculate on what they are doing, its safety, or effectiveness without more details.

“It’s significant that the only targets claimed to work so far are insects feeding on plants. That has huge potential, but all the other applications mentioned in the Tech Review article are speculative in the absence of data.

“As far as I know, academics have limited information about what Monsanto is actually doing, and so we are left with far more questions than answers. This leaves RNA pesticides open to uniformed speculation, from critics as well as supporters.

“The more information Monsanto can provide about the nature of the RNA molecules, off-target effects, stability in the environment etc. the better. This may be a huge advance (and probably is), but we really don’t know.”

Dr Richard Jorgensen, Professor Emeritus in the School of Plant Sciences, University of Arizona

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