Target Pests
Both classes kill a wide range of insects: mosquitoes, flies, ants, cockroaches, fleas, ticks, wasps, beetles, caterpillars, and most other arthropods. Pyrethrins degrade within hours in sunlight. Pyrethroids persist for days to weeks depending on formulation.
Products and Brand Names
Pyrethrins: PyGanic (organic), Evergreen (natural pyrethrin), CB-80 aerosol, many natural flea sprays. Pyrethroids: bifenthrin (Talstar), permethrin (Dragnet), cypermethrin (Demon), deltamethrin (Suspend), lambda-cyhalothrin (Demand CS). The distinction matters for organic certification - only pyrethrins qualify.
Safety and Precautions
Pyrethrins have very low mammalian toxicity and rapid environmental breakdown - among the safest insecticides available. Pyrethroids are also low toxicity to mammals but persist much longer in the environment and are highly toxic to aquatic organisms (fish, invertebrates).
Pro Tips
Side-by-side comparison:
| Property | Pyrethrins (Natural) | Pyrethroids (Synthetic) |
|---|---|---|
| Source | Chrysanthemum flowers | Laboratory synthesis |
| UV stability | Breaks down in hours | Lasts days to weeks |
| Knockdown speed | Very fast | Fast to moderate |
| Residual control | None (hours) | Weeks to months |
| Organic approved | Yes (OMRI listed) | No |
| Fish toxicity | Moderate | Extreme |
| Cost | Higher | Lower |
| Resistance risk | Lower (short exposure) | Higher (prolonged exposure) |
When to use pyrethrins: When you need immediate knockdown with no lasting residue - flushing cockroaches for inspection, treating food areas, organic gardens, quick kill of flying insects indoors. Also when organic certification is required.
When to use pyrethroids: When you need lasting protection - perimeter treatments around homes, lawn pest control, ant barrier treatments, flea yard treatment. The residual activity is the key advantage.
The synergist trick: Most pyrethrin products contain PBO (piperonyl butoxide), a synergist that blocks the insect enzyme that would normally detoxify pyrethrins. This makes pyrethrins 3-5x more effective. Without PBO, pyrethrins are significantly less potent.