Insecticides are used by crop farmers to control insect pests that attack crops. It is a well-known fact that world-wide, some insecticides are losing their effectiveness due to insecticide resistance – i.e. some insecticides no longer kill insects they’re meant to kill. US farmers lost 7% of their crops to pests in the 1940s. Over the 1980s and 1990s, the loss was 13% even though more pesticides (including insecticides) were being used. There are several factors that can cause this but we won’t be considering them here. Rather, we’ll learn how to control pests in such a way that prevents/minimizes insecticide resistance from occurring.

Why is Insecticide Resistance so Bad?

The word tuta absoluta will continue to strike terror into the hearts of tomato farmers. It is a moth – a flying insect that can cause 100% yield loss in tomato farms. Farmers tried to kill these little insects with many different insecticides but to no avail. They have become resistant to those insecticides. That is how bad insecticide resistance can be. I hope you now see why preventing insecticide resistance is very important?

Insecticide Classes and Modes of Action – A Key to Minimizing Insecticide Resistance

Insecticides have different classes and different modes of action. We’re not here to learn scientific terms, so I’ll keep it simple. Our major concern here will be in the modes of action. The mode of action has to do with the way the insecticide act in order to kill the insect. To effectively use insecticides and prevent resistance from developing, rotate insecticides with different modes of action. One way to do this is to use an insecticide twice, but the third time replace it with another insecticide with a different mode of action. You can also combine 2 compatible insecticides with different modes of action.

The table below shows a list of chemical classes and their mode of action. Don’t let those names freak you out. The most important thing is to know chemicals that have different modes of action.

From the table, you can see that Pyrethrins/pyrethroids, Oxadiazines, and semicarbazones have the same mode of action (Sodium Channel Modulation). So you can’t use them alternatively. Rather you rotate them with other chemical with a different mode of action – like OPS/Carbamates, Neonicotinoids or Phenylpyrazoles.

Contact route of entry means that the chemical will kill the insects when it comes in contact with it. So it is important that you target the insects as you spray. Oral route of entry means that the insecticide will kill the insects when the insect ingest it. This can happen when the insect eat leaves, fruits etc that has been poisoned by the chemical.

What follows now will be a list of chemical classes and their active ingredients. Each chemical class have a list of insecticides/active ingredients classified under it. For example, Pyrethrins and Pyrethroids are a chemical class with the following insecticides listed under them: pyrethrins, bifenthrin, permethrin, cyfluthrin, beta-cyfluthrin, deltamethrin, cypermethrin, and lambda-cyhalothrin. Pyrethrins. These active ingredients are what you can buy from Agro-chemical stores. You can’t buy the chemical class in the market.

Caution: Most of these chemicals are harmful to humans and animals. Make sure you follow the manufacturer’s safety instruction such as pre-harvest interval, PHI (time that should pass between insecticide application and harvest) and Reentry Interval, REI (Time that must pass between insecticide application and you or any unprotected person entering the farm). Also wear protective clothing (face mask, respirator, trousers covering your boots, long shirt etc) when applying agro-chemicals. Take extreme precaution because some chemicals are known to cause birth defect, infertility, cancer etc. BeWarned!

The information that follows courtesy of pctonline.com.

1. Chemical Class: Pyrethrins and Pyrethroids.

Active Ingredients: pyrethrins, bifenthrin, permethrin, cyfluthrin, beta-cyfluthrin, deltamethrin, cypermethrin, and lambda-cyhalothrin. Pyrethrins.

2. Chemical Class: Oxadiazines.

Active Ingredients: indoxacarb.

3. Chemical Class: Semicarbazones.

Active Ingredients: metaflumizone.

4. Chemical Class: Organophosphates (OPs) and Carbamates.

Examples of Ops: commonly used by PMPs included chlorpyrifos (Dursban), profenofos, dichlorvos (DDVP), malathion, diazinon, acephate (Orthene), propetamphos (Safrotin) and naled (Dibrom for mosquitoes).

Examples of carbamates once widely used by PMPs include carbaryl (Sevin), bendiocarb (Ficam), and propoxur (Baygon).

5. Chemical Class: Neonicotinoids.

Active Ingredients: imidacloprid, dinotefuran, thiamethoxam, clothianidin and acetamiprid.

6. Chemical Class: Spinosyns.

Active Ingredients: spinosad.

7. Chemical Class: Phenylpyrazole.

Active Ingredients: fipronil.

8. Chemical Class: Avermectins.

Active Ingredients: abamectin, emamectin benzoate and ivermectin.

9. Chemical Class: Diamide.

Active Ingredients: chlorantraniliprole.

Insect Growth Regulators

Insect growth regulators (IGRs) include the juvenile hormone analogs and the chitin synthesis inhibitors. They do not act like the other insecticides mentioned so far. They target mainly young insects and kill them by disrupting critical physiological functions associated with normal insect growth, development and reproduction (egg production).

They are not very toxic to humans but they can affect beneficial insects and some aquatic organism.

10. Chemical Class: Juvenile Hormone Analogs.

Active Ingredients: hydroprene, methoprene, pyriproxyfen and fenoxycarb.

They prevent young/juvenile insects from becoming adults. This can result in death or inability to reproduce.

11. Chemical Class: Chitin Synthesis Inhibitors.

Active Ingredients: diflubenzuron (for control of agricultural pests and termite), hexaflumuron (termite control) and noviflumuron (termite control), Lufenuron (for flea control).

When insects molt, they need something called chintin to form their exoskeletons. Without chintin the insect will die. So what Chitin Synthesis Inhibitors does is to prevent the formation of chintin.

12. Chemical Class: Amidinohydrazone.

Active Ingredients: hydramethylnon (controls cockroaches, crickets and ants).

13. Chemical Class: Pyrrole.

Active Ingredients: chlorfenapyr.

14. Chemical Class: Structural Fumigants. This includes the active ingredient sulfuryl fluoride (for termite control, storage pest control of grains, nuts and dry fruits, soil fumigant against root-knot nematode, building fumigation).

15. Chemical Class: Borates (You may not need this in your farm). This includes the active ingredients borax, boric acid and disodium octaborate tetrahydrate (also used in preventive wood treatments targeted at both wood-destroying insects and fungi). They’re used to control ants, cockroaches.

Insecticides that Act Via Desiccation

16. Chemical Class: Dehydrating Dusts (You may not need this in your farm)

Active Ingredients: silica gels and diatomaceous earth.

They act by making insects’ exoskeletons permeable. The insects that come in contact with these dusts will lose water through their exoskeleton and die by dehydration. They are most effective against crawling insects in dry environments where free water is limited. They are non-toxic to humans but can cause serious respiratory problem if breathed.

Conclusion

After reading this, visit agro-chemical stores in your area and get a list of insecticides with their active ingredients. Classify them base on their mode of action and rotate accordingly. Note that active ingredient is not the name the company gave to the insecticide. It is the chemical that the insecticide contains. For example, SNIPER is the company name of an insecticide with the active ingredient DDVP or dichlorvos (short form for 2,3-dichlorovinyl dimethyl phosphate). Its chemical class is Organophosphate and mode of action is Acetylcholinesterase inhibition.

Following this tip will help prevent/minimize resistance from developing in your farm. Do you have any question? Feel free to ask by commenting. Thanks.