Mode of Action of Insecticides

Classification: Chemical Insecticides –Arsenicals and inorganics-Botanicals –Carbamates-Diamides (pyrazoles) –Dinitrophenols-Formamidines –Fumigants-Benzoylureas –Juvenile hormones-Moulting hormones –Macrolides-Nereistoxin analogues Organochlorines –Neonicotinoids-Organochlorines Oxadiazine/diazoles –Organophosphorus-Oxadiazine/diazoles –Phthalimides-Pyrethroids –Pyrimidine amines-Pyrroles/Pyazoles –Tetramic acids –Tetramic acids-Thiazoles –Urea and thiourea-Miscellaneous

Macrolides Neurotoxicant Cl-Channel blocker Abamectin & analogues Same MOA of Fipronil

GABA-gated channels

Nereistoxin analogues Natural insecticide nereistoxin from Lumbrineris heteropoda. Nereistoxin acts on nicotinic acetylcholine receptors, as partial agonist at low concentration and as channel blocker at higher concentration. Toxic to insects but not lethal to mammalians

Structures

Organochlorines Numerous sub-class Generally neurotoxicant Generally persistent in environment Various side-effects

General structures Halogenated aryl compounds Halogenated cyclodienes DDT Lindane Aldrin Mirex Endosulfan

Mode of action Same as fipronil, abamectin but different site of binding GABA-gated Cl-channel

Oxadiazines/diazoles Neurotoxicant Voltage-dependent sodium channel blocker Indoxacarb Metoxadiazone

Voltage-gated Cl-channel Important of potential propagation in neuron cells Na+ channels both open and close more quickly than K+ channels, producing an influx of positive charge (Na+) toward the beginning of the action potential and an efflux (K+) toward the end.

Pyrimidine amines Mitochondrial complex I electron transport inhibitor Pyrimidifen

MOA of Pyrimidine amines

Pyrroles/Pyrazoles Fipronil: Neurotoxicant, GABA-Cl channel Chlorfenapyr: –Chlorfenapyr has a unique mode of action. It is a pro-insecticide that is converted (or metabolized) to the active form by mixed function oxidases (MFOs) in the target pest. The active form acts on the mitochondria and uncouples oxidative phosphorylation which stops the production of ATP, the primary source of cellular energy.

General structures Pyrroles Chlorfenapyr Pyrazoles Fipronil Pyrazoles Vaniliprole

Metabolic transformation Chlorfenapyr  De-Ethoxymethylation

Oxidative phosphorylation

Tetramic/Tetronic acids Its mode of action is by inhibition of lipid biosynthesis that affects the egg and immature stages of these pests. acetyl-CoA-carboxylase, a lipid metabolism enzyme,16 and causes a significant decrease in total lipids. Tetramic acid Spirotetramet Tetronic acid Spiromesifen

Lipid biosynthesis and AcCoA carboxylase

Urea and Thiourea Urea: Chitin biosynthesis inhibitor Thiourea: ATP synthase inhibitor Urea Sulcofuron Thiourea Diafenthiuron

Metabolic change of activity

Miscellaneous Insecticides Fenoxacrim: Maybe SDH inhibitor Hydramethylnon: ATP biosynthesis Isoprothiolane: Lipid biosynthesis inhibitor: insecticide and fungicide Triazamate: Maybe acetylcholine esterase inhibitor

Structures Isoprothiolane Fenoxacrim Hydramethylnon Triazamate