RNA as a Pesticide and Indemnification

Mike Simpson’s budget rider "Sec 453" to indemnify "pesticides" will even cover RNA sprayed on food crops

I suspect that when you think of RNA technology, the last thing that you think about is that it is being developed as a pesticide to be sprayed on food crops. And of course, you could hardly imagine that any unintended consequences of use in this way might be completely indemnified- in other words, blocked from any legal liability. That there would be no way to sue the developers, manufacturers, distributors, or farmers spraying this material on their crops if a currently pending bill in the US Congress passes.

I refer to Idaho Congressman Mike Simpson’s (Idaho's 2nd congressional district) rider to the FY26 Interior and Environment Bill, known as Section 453. Aspects of this bill were covered previously in two preceding Substack essays.

and

“The Deadly Campaign to Shield All Pesticides from Legal Liability”

Here is the actual text of the rider that Congressman Mike Simpson is trying to slip into the bill:

Pesticides

Sec. 453. None of the funds made available by this or any other Act may be used to issue or adopt any guidance or any policy, take any regulatory action, or approve any labeling or change to such labeling that is inconsistent with or in any respect different from the conclusion of—

(a) a human health assessment performed pursuant to the Federal Insecticide, Fungicide, and Rodenticide Act (7 U.S.C. 136 et seq.); or

(b) a carcinogenicity classification for a pesticide.

Keep in mind that herbicides such as Roundup (Glyphosate) are classified as pesticides. “Pesticides” is an incredibly broad legal category under current federal law. Based on this draft congressional wording, the category of “Pesticides” includes both current and future “Pesticides” and “Herbicides.” All current and future “pesticides” would be covered under this bill. One new technology being used as a “pesticide” involves spraying double-stranded RNA on plant leaves to trigger an RNAi pathway. RNAi = interfering RNA. This is RNA that can be used to block the function of other RNA molecules in a sequence-specific manner.

This bill is carefully worded to evade detection of meaning and intent, but these are the practical consequences if this rider survives and the bill passes:

• It specifically restricts carcinogenicity classifications for pesticides [defined to include herbicides], something that was likely put in to shield pesticide manufacturers and strengthen their FIBRA defense (that they did not “fail to warn” because they simply followed the EPA’s advice and had no option to do anything else).

• The language throughout the first paragraph is incredibly broad (e.g., “none of the funds made available by this or any other Act”), something which is quite unusual and easily abused in the courts.

• This greatly restricts the EPA’s (already incredibly slow) ability to update existing toxicity assessments for these chemicals (as those new FIBRA assessments would differ from an already existing assessment). Put differently, within this framework, if concerning toxicity data emerges, it will take years for anything to be done about it.

• If another agency or process (e.g., from the Clean Water Act) determines a pesticide is hazardous, FIFRA having previously concluded the pesticide was “safe” could be used to block the new findings from being implemented.

• By including “any guidance or policy” this arguably broadens FIBRA’s coverage to the other warnings (signs where pesticides are sold) states can give about pesticides and restricts their ability to limit pesticide usage.

• In many cases, both states and the Federal government rely upon Federal funding to address pesticide issues (e.g., educating farmers in their risks and safe use). As worded, that can no longer occur.

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Mike Simpson of Idaho and the Potato Beetle

Is there anything particularly significant about Congressman Mike Simpson? Well, he represents one of the top potato-growing regions of the United States and the world. He certainly is one of many congresspersons who represent regions closely tied to big ag. So why is he so focused on providing indemnification for “pesticides” and their manufacturers, as opposed to, say, congresspersons from Ohio, Kansas, Missouri, Wisconsin, or any one of the many states with large stakes in big ag?

None of those are tied to the potato industry in the way that Idaho is. Why is this bill particularly relevant to the potato crop?

The answer may lie in the curious case of the potato beetle.

The Colorado potato beetle (Leptinotarsa decemlineata), commonly referred to as the potato beetle, is one of the most significant insect pests affecting the potato growing industry in Idaho, where potatoes are a cornerstone crop contributing billions to the state's economy. As the top U.S. potato producer, Idaho accounts for approximately 30% of the nation's potato output, with a production value exceeding $1 billion annually in recent years. The beetle's feeding behavior poses ongoing challenges, but through integrated pest management (IPM) strategies, its impacts are largely mitigated, though resistance to insecticides remains a growing concern

Biological and Direct Impacts of the Potato Beetle on Crops

• Damage Mechanism: Both adult beetles and larvae feed voraciously on potato foliage, stems, and occasionally tubers, leading to defoliation that reduces photosynthesis and tuber bulking. Larvae are particularly destructive, consuming about four times more leaf material than adults. If left uncontrolled, this can result in 70-100% defoliation, plant death, and yield losses of up to 40%.

• In Idaho, the beetle typically completes two generations per season, with overwintering adults emerging in spring to infest fields, exacerbating damage during critical growth stages like bloom and tuber formation.

• Plants can tolerate varying levels of defoliation (e.g., 30-40% pre-bloom, up to 100% post-bulking), but repeated infestations weaken crop health and quality.

• Prevalence in Idaho: The beetle is widespread across Idaho's potato-growing regions, though population pressure is generally lower compared to eastern states like Wisconsin due to factors such as climate and lower genetic diversity in local beetle populations.

• No major outbreaks were reported in Idaho for 2025, but cull potato piles and alternative hosts like nightshade weeds can serve as reservoirs, allowing populations to build if not managed.

Economic and Industry-Wide Impacts

• Yield and Cost Implications: Uncontrolled infestations directly reduce marketable yields, with historical data indicating potential 40% losses that translate to substantial revenue shortfalls for growers.

• Beyond yield, the beetle drives up production costs through repeated insecticide applications, scouting, and alternative controls. For instance, resistance to common insecticides has led to increased expenses, with some U.S. regions seeing annual added costs of $15-20 million for managing resistant populations—trends that could affect Idaho if resistance escalates.

• In 2025, Idaho's potato acres were forecasted to decline by about 4% nationally, though this is attributed more to market factors than beetle pressure alone.

• Broader Economic Ripple: Potato production and processing represent over 15% of Idaho's income, amplifying the beetle's indirect effects through job impacts in farming, processing, and export sectors.

Management and Mitigation Efforts

• Current Strategies: Idaho growers rely on integrated pest management practices (IPM), including chemical controls, crop rotation to disrupt beetle dispersal, elimination of volunteer potatoes and weed hosts, and scouting with economic thresholds (91% of growers scout fields).

• Rotating modes of action (MOA) of pest management practices is vital to delay resistance.

• There are some biological strategies, including the fungus Beauveria bassiana (which can reduce populations by up to 75%) and predators like lady beetles, support conservation efforts.

• Resistance Challenges: The beetle has developed resistance to over 50 insecticide active ingredients globally, including neonicotinoids and pyrethroids, driven by overuse and genetic adaptation.

• Experts warn that resistance to commonly used insecticides is inevitable without continued vigilance.

• Transgenic potato varieties and breeding for resistance traits from wild Solanum species are also advancing, potentially reducing reliance on chemicals.

Overall, while the Colorado potato beetle continues to exert pressure on Idaho's potato industry through potential yield reductions and control costs, effective IPM and innovative solutions have prevented it from causing widespread disruption in 2025. Sustained monitoring and diversified approaches will be key to maintaining this balance amid evolving resistance risks.

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Biotech companies and their investors, as well as the Big Ag view emerging tools like RNA-interference bioinsecticides (e.g., Calantha™ with ledprona), which provide targeted control effectively decreasing beetle populations, as the way forward.

What is Ledprona?

(Text below is primarily sourced from GROK)

Ledprona is the active ingredient in Calantha™, the first commercially registered sprayable double-stranded RNA (dsRNA) biopesticide designed to control the Colorado potato beetle (Leptinotarsa decemlineata), a major pest of potato crops.

Developed by GreenLight Biosciences, ledprona utilizes RNA interference (RNAi), a natural gene-silencing mechanism found in plants and animals, to target the beetle’s proteasome subunit beta type-5 (PSMB5) gene. This gene is essential for producing a protein critical to the beetle’s survival, part of the ubiquitin/proteasome machinery that removes damaged proteins from cells.

After being sprayed on potato plants, when the Colorado potato beetle eats the leaves it also ingests the dsRNA. Ledprona’s dsRNA is then processed by the insect’s RNAi pathway, leading to the degradation of PSMB5 mRNA. This reduces PSMB5 protein levels, causing toxic buildup of metabolic waste, which stops the beetle from feeding and ultimately leads to its death. Laboratory studies have shown that a concentration of 25×10⁻⁶ g/L of ledprona can achieve 90% mortality in second-instar larvae within six days of exposure.

During the RNA interference (RNAi) process, the double-stranded RNA (dsRNA) is cut into small interfering RNA (siRNA) by the Dicer enzyme. The siRNA is incorporated into the RISC enzyme complex serving as the template for matching sequences which are then degraded by RISC.

The biopesticide has demonstrated efficacy comparable to conventional insecticides like spinosad in greenhouse and field trials. Approved by the U.S. Environmental Protection Agency (EPA) in December 2023 for a three-year period, ledprona is classified by the Insecticide Resistance Action Committee (IRAC) under Group 35 (RNAi-mediated targeted suppressors), representing a novel mode of action.

The manufacturer claims that the high specificity minimizes harm to non-target organisms, such as pollinators, and that it degrades quickly in the environment, supporting biodiversity and sustainable pest management. Ledprona is applied as a foliar spray, compatible with standard potato farming practices, and is part of integrated pest management (IPM) strategies to combat insecticide resistance, particularly in regions like Idaho, where the beetle is a significant threat.

However, some environmental groups, like the Pollinator Stewardship Council, have raised concerns about potential unintended ecological impacts, citing insufficient research on non-target species.”

See the EPA docket at www.regulations.gov (EPA-HQ-OPP-2021-0271) for further details.

Chemical and Engineering News provides further coverage of this temporary authorization here.

See this press release for further information about the use of this technology as a pesticide in greenhouses.

Here is an early peer-reviewed academic publication describing this technology and application:

First Sprayable Double-Stranded RNA-Based Biopesticide Product Targets Proteasome Subunit Beta Type-5 in Colorado Potato Beetle (Leptinotarsa decemlineata)

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How unique is the proteasome subunit beta type-5 (PSMB5) gene?

PSMB5 is far from unique at the functional or broad sequence level, showing high conservation that underscores its evolutionary importance. The proteasome subunit beta type-5 (PSMB5) gene encodes a core catalytic subunit of the 20S proteasome, which is responsible for protein degradation in the ubiquitin-proteasome system.

This gene is highly conserved across eukaryotes, reflecting its essential role in cellular proteostasis, but it exhibits sequence variations that can be exploited for species-specific applications, such as RNA interference (RNAi) in pest control.

What could go wrong?

The major risk is that this biopesticide affects non-target species. Although some rudimentary testing was done on some target species - such as honey bees, as well as some attempts at epidemiologic genetic testing of insects that might be affected by this biopesticide, it is estimated that there are 5.5 million insect species in the world. The testing didn’t scratch the surface in determining what other insects might be negatively impacted. If something goes wrong, it could have far-reaching consequences for entire populations and ecosystems. Not just in this country, but in other countries, that rely on the United States for regulatory guidance.

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The product has not been widely tested for interference with the PSMB5 from other species. If Mike Simpson’s rider passes, and some complication develops that compromises crop safety, leads to the development of resistant potato beetles, or impacts on other insect (or mammalian) species, there will be no legal liability or pathway for remedy.

What this example illustrates is the dangers inherent in this type of broad indemnification legislation. The use of Ledprona technology for spraying on crop leaves may be completely benign. Or there may be unforeseen adverse effects.

But what about the next “cool” bio- or chemical “pesticide” technology? As we all experienced during the COVID-19 crisis and the indemnification provided to vaccine manufacturers, unintended consequences happen when introducing new technology. And the blowback can be pretty harsh.

Please contact your congressional representative, your Senators and the White House. Let them know that broad, forward-looking liability protection for industries and broad categories of biochemical agents is a bad idea, and that Mike Simpson’s rider is completely contrary to the principles of the Make America Healthy Again movement.

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It appears that the EPA period for public comments on Ledprona is closed. But below is the EPA page with links to the regulatory approvals.

https://www.regulations.gov/search?filter=EPA-HQ-OPP-2021-0271