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Chemical Classes and Their Modes of Activity

August 18, 1999

Entomologists emphasize that you should be sure to rotate insecticides. Rotating insecticides/miticides helps to ensure their longevity and effectiveness, and they minimize the potential for the development of resistant pest populations. It is important to understand how insecticides/miticides work on insect and mite pests that attack landscape and nursery plants so the appropriate materials can be used.

Insecticides/miticides are separated into different chemical classes based on their mode of activity. The chemical classes of materials used in the landscape and nursery include chlorinated hydrocarbons (organochlorines), organophosphates, carbamates, pyrethroids, macrocyclic lactone, chloronicotinyls, insect growth regulators, and soaps and oils. Common insecticides/miticides used in landscapes and nurseries and their chemical classes are presented in Table 1. Chemical classes and their modes of activity are categorized in the following six groups:

  1. Organophosphates and carbamates work by inhibiting the enzyme cholinesterase, which pre-vents the termination of nerve impulse transmission.
  2. Chlorinated hydrocarbons and pyrethroids work by destabilizing nerve cell membranes.
  3. Macrocyclic lactone affects gamma-amino butyric acid (GABA)–dependent chloride ion channels, which inhibits nerve transmission.
  4. Chloronicotinyls work on the central nervous system, causing overstimulation and blockage of the postsynaptic nicotine acetylcholine receptors.
  5. Insect growth regulators are chitin synthesis inhibitors or juvenile hormone mimics. Chitin synthesis inhibitors prevent the formation of chitin, an essential compound of an insect’s exoskeleton. Juvenile hormone mimics cause insects to remain in a young life stage.
  6. Soaps and oils work by damaging the waxy layer of the exoskeleton of soft-bodied insects, resulting in desiccation (drying), or by covering the breathing pores (spiracles) of insects, resulting in suffocation.

Several chemical classes have very similar modes of activity. The organophosphates and carbamates, despite being different chemical classes, both have similar modes of activity (they are acetylcholineste-rase inhibitors). So using acephate (Orthene), then switching to bendiocarb (Dycarb, Turcam), is not a proper rotation scheme. Similarly, chlorinated hydrocarbons and pyrethroids have identical modes of activity (they affect nerve cell transmission). In this case, using dicofol (Kelthane), then switching to bifenthrin (Talstar), would not be a proper rotation scheme. Examples of rotating different chemical classes include:

Dursban->Talstar->insecticidal soap->Diazinon (Group: 1->2->6->1)>/P>

Orthene->Tame->Avid->Mesurol (Group: 1->2->3->1)

Avid->horticultural oil->Kelthane->insecticidal soap (Group: 3->6->2->6)


*This is a total eradication rotation.

Rotating different chemical classes with varied modes of activity helps extend the longevity of currently available insecticides and leads to less chance that insect and mite populations will develop resistance.

Author: Raymond Cloyd


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