Derris

Also called Rotenone. A dust made from the root of Derris elliptica. A biocide (often inaccurately called a pesticide) that is used to kill insects and acarids such as aphids, thrips, red spider mites, itchmite etc.

The potency of derris is short-lived, because it breaks down quickly. However, it is dangerous because it is particularly poisonous to humans and fish.

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It has an LD50 of 39. The LD50 is a measure of the lethal dose required to kill 50% of the population.

The LD50 may be a skin one or an oral one etc and may have been tested on an animal with similar digestion, metabolism etc to humans, such as rats. So it means that a group of rats would have to eat 39 milligrams of derris per kilogram of bodyweight for half of them to die from it.

This is then converted to a lethal dose to 50% of the people in a sample - that means it would be expected to kill half of the people who ate 39 mg of derris for every kg of their own bodyweight. So if 100 adults ate 39 mg of rotenone for every kg of their own bodyweight, 50 of them would be expected to die.

Derris's LD50 of 39 means that it is very poisonous. The lower the number, the less it takes to kill. This means it would take around 3 g of derris to have a 50:50 chance of killing an average adult male weighing 80 kg (176 lb or 12½ stone).

It is calculated is by multiplying the LD50 by the body weight. The units of the answer are milligrams or mg. So, if it comes to more than 1000 mg, divide the result by 1000 to get the number of grams or g.

39 x 80 = 3120 mg

3120/1000 = 3.12 g
It is often touted as being non-harmful to mammals or birds. You wouldn't tuck into a derris burger every night and although it breaks down quickly in the environment, it may not break down quickly in you.

Derris has also been linked to Parkinson's disease and other illnesses, so it is not just the possibility of death.

If you use it, use it with care because it is poisonous to you and your customers. Also it is a broad-spectrum biocide. This means that it kills a wide range of organisms. This means it will kill more of the ones you are not setting out to kill, including the good guys who keep your pests down.

My thanks to RDF who spotted some inaccuracies in an early version of this web page
Generally biocides kill far more desirable organisms than they do pests. This is because pests are only a tiny percentage of the insects or similar species on your farm - typically around 1%.

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This page was updated on December 27, 2007