Pyrethroids, Pyrethrins & Pyrethrums – Insecticide Profile

The following is a guide written to assist people who are looking to find out more about pesticides and their effects on bees. This should be used as generic educational advice only and does not alter your obligation to follow local laws and rules, on top of safety requirements relating to the application of insecticides. If you have any submissions to add to this post, or requests to amend its contents, please email me at

Pyrethroids? Pyrethrins? Pyrethrums? Which one is it?

I will start this profile by clearing up the definitions of Pyrethroids, and how they differ from Pyrethrins and Pyrethrums (even though the terms are often used interchangeably). Pyrethroid is a generic term used to describe compounds which have been made to mimic Pyrethrins which were naturally found in flowers we used to call Pyrethrums, but now call Chrysanthemums. The term “Pyrethrum” can be used to refer to Pyrethrins, especially when trying to emphasise that the chemical originated from the Chrysanthemum plant.  Long story short:

  • Pyrethrums = the flower, and sometimes refers to the natural insecticide inside the Chrysanthemum flower.
  • Pyrethrins = the natural insecticide which comes from the Chrysanthemum flower.
  • Pyrethroids = organic compound (which are usually synthetic) chemicals based on the insecticide which comes from Chrysanthemum flower. They are generally considered the most effective of this group of insecticides.

I will again emphasise that you will often find these terms used interchangeably, which causes me (and anyone I talk to) a great deal of confusion.

How do they work?

Pyrethroids have very potent insecticidal effects, and essentially work by blocking the insect’s nervous system ability to operate properly, which in turn permanently paralyses the insect.  There is also evidence to suggest that sub-lethal doses of pyrethroids may repel insects, and can have weird side effects on insects, however these are openly debated in several forums. Bees are particularly sensitive to pyrethroids , requiring as little as 0.02 micrograms to be killed. On top of that, pyrethroids kill small larvae of water dwelling insects in doses as little as four parts per trillion. This leads to water dwelling fish, birds and other animals without vital sources of food, and can doom local rivers and streams. Certain pyrethroids have been shown to decrease bee fecundity (or their effectiveness at reproducing).

You may see piperonyl butoxide as a common ingredient to products containing pyrethrins and pyrethroids. This is because piperonyl butoxide is a synergising agent, and makes the overall product a more effective (see: lethal) insecticide.

What products use pyrethroids and pyrethrins?

Most brands and companies have product lines which use pyrethroids (or their siblings), and are usually marketed as “natural” or “eco-friendly” insecticide methods. Due to their “natural” source, pyrethrins are utilised in a lot of organic food growth. However, it is very important to remember that just because a product is sourced from nature, does not instantly make it beneficial or healthy. I personally always find it ironic that anyone is allowed to market a product with the express purpose if killing insects as “eco-friendly” (but the cynic in me is not at all surprised). If you would like to see an ever growing list of products I have found to contain pyrethrins and pyrethroids, please visit my Wall of Shame post.

A rule of thumb is that if you see a chemical ending in “thrin” on the label, it is likely a pyrethroid or pyrethrin. If you see a product which includes any of the following, it likely contains a pyrethroid or pyrethrin:

How do I know whether bees are being impacted by Pyrethroids or Pyrethrins?

The following is a short list of signs or symptoms you may see as a result of pyrethroid/pyrethrin poisoning. It is important to remember that majority of bee species are solitary, and you will not likely witness the effect insecticides on them unless you literally stand and watch the plant all day. The other factor is that many social bees (including the honeybee) will avoid or be unable to return to their hive once poisoned, and you may not see these symptoms back at a beehive. Just be aware that just because you cannot see the signs below, does not mean that they are not occurring.

You may see a combination or variation on any other following:

  • Regurgitation of honey stomach contents and tongue extension in honeybees  (caused by organophosphates and pyrethroids)
  • Excessive numbers of dead and dying bees in the area (many insecticides can cause this symptom).
  • Increased defensiveness of honeybee hives (most insecticides can cause this symptom)
  • Lack of foraging bees on a normally attractive blooming crop (most insecticides can cause this symptom)
  • Immobile, lethargic bees unable to leave flowers (many insecticides can cause this symptom)

Minimising impact on the bees

The effects pyrethrins and pyrethroids are generally limited to less than a week, however dosage and application methods greatly impact the timeframe of Extended Residual Toxicity (ERT – or an expected mortality rate of 25%). Some mixtures can have toxic effects to bees for only a few hours , and careful use can limit the impact on bee populations. If you must use a pyrethroid or pyrethrin product, it is generally recommended to apply them:

  • in the evening, when it is unlikely for bees to be pollinating.
  • to affected areas of the plant only, and avoid coating the entire plant (especially the flowers) where possible.
  • when the plant is not in bloom (e.g. after flowers have wilted and dropped from the plant).
  • after warning or informing any beekeepers you may know in the area (however, this will only protect a small number of honeybees, and will still impact other types of bee).
  • if you have explored other ways of controlling the target pest (e.g. attracting or introducing ladybugs to control aphids or planting predator attracting plants)

If you operate a farm, nursery, orchard or agricultural centre, consulting with local beekeepers and researching local types of beneficial insects that you may be affecting are massive steps to ensuring you are making informed decisions about how you interact with the local fauna.

As a consumer, buying products that are sourced from places which responsibly use pesticides or limit their use entirely, is an effective way to “vote with your wallet” and influence stockists and suppliers.

Personally, I find that most people are horrified when they find out that a product they use is likely harming bees. Politely and calmly informing people of the effects of products they use may be all you need to do to influence people you know and get them to rethink their gardening habits.

In Conclusion

I can personally see the draw that people have to pyrethroids (and their siblings). They are seemingly natural (or inspired by nature) and have no distinct toxic effects to pets (unless we are referring to aquatic pets) or humans. They also work, killing a wide range of insects relatively quickly and can be applied using a large variety of different methods for added convenience.

What is overlooked is the fact that regardless of where it came from, this pesticide is very toxic to most insects, including the good ones. A chemical that was once used by once specific flowering plant to defend itself from insects munching on it, is now being sprayed on a huge range of gardens and agriculture across the planet. I would caution those who use these types of chemicals, and at the very least recommend doing your own research before using these products yourself.

One thought on “Pyrethroids, Pyrethrins & Pyrethrums – Insecticide Profile

  1. Hi,
    I recently put in pryrethrum in the garden but have since been told it kills bees. I believe the person was referring to insecticides made from pyrethrins or pyrethroids but wanted to be sure. Can’t seem to find much on the subject except that bees do act as a pollinator for pyrethrum so I’d assume it is safe in thus form. Are you able to shed any light on this?


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