Lab · Technology
RNAi pesticides and biological controls
What is rnai pesticides and biological controls?
Two groups of actives that work through biology rather than broad nerve toxicity. RNA interference products are double-stranded RNA that shuts off one essential gene in the target pest. Biologicals are living or natural agents, such as Bti bacteria against mosquito larvae and Beauveria fungus against bed bugs. Both act narrowly, and both have hard limits.
Reviewed by LTK editorial team
Where it fits
- Mosquito larvae in standing water where non-target exposure matters. EPA describes Bti as a soil bacterium whose toxins affect only the larvae of mosquitoes, black flies and fungus gnats. EPA also reports minimal toxicity to honey bees, none to people, and no documented resistance to Bti as a larvicide.
- Bed bug programmes that need a residual barrier with a different mode of action. Beauveria spores are applied as bands that bugs walk across on their way to a host. In lab testing over residues of 22 insecticides, bed bug kill seven weeks after application was not harmed overall, even where the residues cut spore viability.
- Knowing what the first registered RNAi spray actually covers. EPA registered ledprona in December 2023 for three years. It is a sprayable double-stranded RNA that kills Colorado potato beetle by silencing the gene for one protein, PSMB5. EPA found no risk of concern to human health or the environment, including listed species.
- Resistance-management planning. EPA gives resistance management as one reason it supports the technology, because a gene-silencing active does not share a mode of action with conventional insecticides.
Where it does not
This is the part the brochure leaves out, so it is the part worth reading.
- Assuming RNAi cannot be resisted. Researchers selected a Colorado potato beetle population in about nine rounds of selection that survived more than 11,100 times the dose that killed susceptible beetles. The resistance also covered a second, different dsRNA target, which means it blocks the RNAi mechanism in general, not just one gene. Rotating to another dsRNA may not help.
- Structural or urban use today. The registered RNAi spray is labelled for Colorado potato beetle on potatoes, and the label is the law. A structural RNAi product is something to watch for, not something you can buy and apply.
- Fungal biocontrol of subterranean termites. In 50 years of attempts, mostly with Metarhizium, no successful field use has been reported. Colonies eat infected nestmates when deaths are low and bury them when deaths are higher, so the fungus never produces spores. Overwhelming that took spore densities two to three orders of magnitude above what occurs naturally in soil.
- Adult mosquito complaints. Bti works only on larvae that eat it in the water. It does nothing to the adults biting the customer tonight.
- Fungal barriers on bare wood, or over old DIY sprays, if you expect them to keep working. Spore germination on wood fell to 29% by seven weeks, compared with 64–69% on fabric. Residues of 12 of the 22 insecticides tested significantly reduced spore viability at five weeks.
Sources
- EPA Registers Novel Pesticide Technology for Potato Crops — U.S. EPA (2023)
- Bti for Mosquito Control — U.S. EPA
- Selection for high levels of resistance to double-stranded RNA (dsRNA) in Colorado potato beetle using non-transgenic foliar delivery — Scientific Reports (2021), PMC7985369
- When Subterranean Termites Challenge the Rules of Fungal Epizootics — PLOS One (2012), PMC3314638
- Effects of Chemical Insecticide Residues and Household Surface Type on a Beauveria bassiana-Based Biopesticide for Bed Bug Management — Insects (2021), PMC7998477
