Pyrethrin has two characteristics that matter enormously for bed bug control. It can kill susceptible bed bugs by disrupting their nervous system, but it also breaks down relatively quickly and faces a resistance problem in some bed bug populations.
Yes, pyrethrins can kill bed bugs. EPA lists pyrethrins among the pesticide classes registered for bed bug control and says they can kill bed bugs and flush them from hiding places. The limitation is resistance: some bed bug populations are resistant to pyrethrins and pyrethroids, so a pyrethrin product should not be assumed to work against every infestation.
Pyrethrin products also commonly contain a synergist such as piperonyl butoxide, or PBO. That combination can make pyrethrins more effective against susceptible insects, but PBO cannot overcome every mechanism of insecticide resistance.
Pyrethrins and Pyrethroids Aren’t the Same Thing
Pyrethrins are botanical insecticides derived from chrysanthemum flowers. Pyrethroids are synthetic insecticides designed to act in a similar way.
Both interfere with normal insect nervous-system function, and EPA groups pyrethrins and pyrethroids among the major pesticide classes used against bed bugs.
The natural-versus-synthetic distinction does not tell you which product will work against a particular infestation. The active ingredient, formulation, application site, label directions, and susceptibility of the bed bug population matter much more.
If you are comparing chemical classes rather than one ingredient, what chemicals kill bed bugs covers the broader options.
Pyrethrins Break Down Quickly in Sunlight
One genuine limitation of natural pyrethrins is their environmental persistence.
Pyrethrin I breaks down rapidly when exposed to sunlight. NPIC reports a half-life of 11.8 hours in sunlit water and 12.9 hours on soil surfaces. On potato and tomato leaves, less than 3% remained after five days.
Without light, degradation can be substantially slower.
Those figures should not be treated as a universal residual-life calculation for every indoor pyrethrin spray. Formulation and application conditions matter. They do, however, demonstrate why pyrethrins are considered relatively short-lived compared with many synthetic pyrethroids.
That rapid environmental breakdown is separate from the reason piperonyl butoxide is added to many pyrethrin products.
Piperonyl Butoxide Doesn’t Protect Pyrethrin From Sunlight
Piperonyl butoxide is a synergist, not a stabilizer whose primary job is shielding pyrethrin from photodegradation.
Insects possess enzymes capable of breaking down certain insecticides. PBO inhibits some of those detoxification enzymes, allowing the insecticide more opportunity to exert its effect.
PBO itself is not intended to kill the insect. Its value comes from making certain insecticides more effective when the two are used together.
That is why pyrethrins frequently appear alongside PBO or another synergist in pesticide formulations. NPIC specifically notes that insecticides containing pyrethrins often contain PBO or another synergist.
Current EPA bed bug registrations provide real examples. EPA’s bed bug product database includes registered products containing both pyrethrins and PBO.
The important distinction is simple: sunlight can break down pyrethrins outside the insect, while PBO interferes with enzymatic detoxification inside the insect. Those are different processes.
PBO Can Help With Some Resistance Without Eliminating It
Bed bug resistance makes the PBO story more complicated.
A peer-reviewed study tested PBO against three field-collected bed bug strains while examining resistance to deltamethrin, a synthetic pyrethroid. Two of those strains had resistance ratios exceeding 2,500-fold before synergism.
PBO significantly increased susceptibility to deltamethrin in all three strains, but the size of the effect differed substantially among populations.
Most importantly, PBO did not restore the two highly resistant strains to normal susceptibility. After treatment with the synergist, substantial resistance remained.
That tells us something important about resistance itself. Blocking one detoxification pathway can make an insecticide considerably more effective when that pathway contributes to resistance, but bed bugs can possess additional resistance mechanisms that PBO does not remove.
The wider problem is covered in why bed bugs are becoming resistant to pesticides.
Pyrethrins With PBO Also Failed Against One Highly Resistant Strain
The same study provides an even more relevant result for pyrethrins themselves.
Researchers exposed one of the highly resistant bed bug strains to a formulated pyrethrin product containing PBO. The synergized pyrethrins did not produce a significant increase in mortality compared with PBO alone in that strain.
That does not establish that pyrethrin plus PBO fails against every bed bug population. The experiment involved a particular highly resistant field strain.
It does demonstrate why the presence of a synergist should never be treated as a guarantee that resistance has been solved.
EPA currently makes the broader point directly: Some bed bug populations have become resistant to pyrethrins and pyrethroids. Where resistance exists, these insecticides may flush bed bugs from their harborages without killing them.
A Registered Pyrethrin Product Can Still Be a Legitimate Bed Bug Pesticide
Resistance does not mean pyrethrins have ceased to be real bed bug insecticides.
EPA continues to list pyrethrins as a pesticide class registered and used for bed bug control. Its database also contains registered bed bug products with pyrethrins among their active ingredients.
The correct conclusion is narrower: pyrethrin can kill susceptible bed bugs, but its performance depends on the product and the susceptibility of the population being treated.
That is also why treatment failure does not automatically prove resistance. EPA notes that resistance can only be confirmed through laboratory testing, and inadequate application, missed harborages, failure to follow up, and other treatment problems can also allow an infestation to persist.
For an established infestation, we would not build the entire treatment strategy around the assumption that one pyrethrin product will solve it. Bed bugs are difficult to eliminate for several overlapping reasons, and resistance is only one of them.
Questions About Pyrethrin and Bed Bugs
How can you tell whether a product contains pyrethrins or a pyrethroid?
Read the active-ingredient section of the pesticide label. Natural pyrethrins are generally listed as “pyrethrins,” while pyrethroids appear under their individual chemical names, such as permethrin or deltamethrin.
Can you add extra PBO to a pyrethrin pesticide yourself?
Do not alter a pesticide formulation or mix pesticides in ways the labels do not permit. Use the product only at its labeled concentration and according to its application directions.
Does plant-derived mean pyrethrin is safer than synthetic pyrethroids?
No. “Natural” does not establish that a pesticide is harmless. Pyrethrins can affect people, pets, and non-target organisms, and the risks depend on exposure and the particular formulation. Follow the product label regardless of whether the active ingredient originated from a plant.
Does pyrethrin resistance mean permethrin will fail too?
Not automatically. Resistance patterns differ among bed bug populations and active ingredients. However, cross-resistance within pyrethrins and pyrethroids is a legitimate concern, so repeated failure with products from the same chemical class is a reason to reconsider the treatment strategy rather than simply applying more.