It all started with Chrysanthemums.  These types of flowers have a naturally occurring pesticide component that is mildly toxic to insects but also highly repellent.

While there are many types of chrysanthemums (mums) …

Pyrethrins are made from chrysanthemums typically grown in the highlands of East Africa.  (Chrysanthemum pyrethrum cinerariaefolium)

Pyrethrins are an oil based extract or sometimes a synthetic compound chemically similar to the extract.

There are several esters present in extracts produced from chrysanthemums grown for this purpose.  Pyrethrins contain one or more of these esters:  pyrethrin I, pyrethrin II, cinerin I and cinerin II

Many people are allergic to mums.

Extracts from chrysanthemums have a very strong perfume odor.

To be effective as an insecticide, pyrethrin extracts are mixed with chemical solvents and a chemical synergist which are both more toxic than the pyrethrin itself.

Pyrethrins have a very short residual life and are best used on something where all or most all of the insects are present at the time of application – such as a hornet’s nest.

Since pyrethrins are highly repellent to insects is typically causes a very violent reaction from stinging insects – only apply ay night, do not shine a light on the nest – and be ready to run.

Pyrethroids

There have been several ‘generations’ of chemicals synthesized from the pyrethrin base model.  These synthesized materials typically have a lower acute toxicity, little or no odor (depending on formulation), and they have a longer residual life.

The problem that some people have with the synthetic versions are twofold.  One, they are synthetic.  (Please see Synthetics for a information on the pro and cons of natural and synthetic materials.) Two, these materials have a longer residual life.  (Please see Residual for a information on the role of residue and persistence.).