Muscle and nerve affecting insecticides
The most common insecticides are those that affect the muscles and nerves. This is one of five ways insecticides work.
Muscle and nerve affecting insecticides tend to be fast acting.
Technically, systemic insecticides refer to how they act on the body, not their mode of action ie nerves and muscles. However, most systemic insecticides are nerve and muscle distuptors.
They are but one of five ways that insecticides work. To read about the other four modes of action, click here.
In the Muscle and Nerve affecting insecticides group there are a host of classifications each of which are based on particular neural pathways. These include:
Acetylcholinesterase (ACHE) Inhibitors;
Gaba-Gated chloride channel blockers;
Sodium channel modulators;
Nicotinic acetylcholine receptor competitive modulators;
Nicotinic acetylcholine receptor allosteric modulators; and
Glutamate-Gated chloride channel allosteric modulators.
Each of these neural pathways are activated by a class of chemicals such as organophosphates. And each of those classes have a host of active ingredients.
Muscle and nerve affecting insecticides therefore work in a number of ways including causing neurons to continue to fire or to stop firing. They tend to cause lethargy and paralysis in insects.
Some examples for nerve affecting insecticides
From the IRAC site, (IRAC – Insecticide Resistance Action Committee) we can see a nerve affecting Sodium Channel Modulator with active ingredients such as pyrethroids, pyrethrins and DDT.
Generally, pyrethroids are synthetic renditions of the naturally occurring pyrethrins. Natural pyrethrins come from flowers in the genus Chrysanthemum cinerariifolium. Pyrethrum is a plant within that genius.
One particular pyrethroid is Acinathrin. It’s an insecticide that’s currently used to control the Varroa mite affecting bees worldwide (except Australia). However, as often occurs, the Varroa mite is becoming resistant to that active ingredient. For an understanding of resistance in plants read my blog: Susceptible and resistant plants: what are they and how do they work?
Pyrethrins and pyrethroids are usually delivered as a contact insecticide. They are typically contact killers readily absorbed into the system of the insect.
All of these insecticides are extremely toxic and unconscious or reckless use will cause the death of any insect that comes in contact with them. Some insects (eg whitefly) have been resistant to synthetic pyrethroids for more than 20 years.
Many of us have heard of the notorious Neonicotinoids. This class of insecticide is so frequently used it’s scary. I’ve been in retail outlets and have heard customers speak about mundane issues such as aphids on and have had to hold my jaw as I hear the sales person recommending a Neonicotinoid as a remedy! Talk about overkill! More on that later!
According to IRAC, the key active ingredients in the Neonicotinoid groups are: Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Nitenpyram, Thiacloprid, Thiamethoxam. This class of chemicals are often used in systemic insecticides. Typically, the leaves are sprayed, the plant absorbs the active ingredients and transports these throughout the plant. Anyone who feeds off the plant is poisoned.
Another insecticide mode of action is inhibiting growth.