Organochlorine

Most act on neurons by causing a sodium/potassium imbalance preventing normal transmission of nerve impulses. Some act on the GABA (γ-aminobutyric acid) receptor preventing chloride ions from entering the neurons causing a hyperexcitable state characterized by tremors and convulsions. Usually broad-spectrum insecticides that have been taken out of use.

Organophosphate

Cause acetylcholinesterase (AChE) inhibition and accumulation of acetylcholine at neuromuscular junctions causing rapid twitching of voluntary muscles and eventually paralysis. A broad-range insecticide, generally the most toxic of all pesticides to vertebrates.

Organosulfur

Exhibit ovicidal activity (i.e., they kill the egg stage). Used only against mites with very low toxicity to other organisms.

Carbamates

Cause acetylcholinesterase (AChE) inhibition leading to central nervous system effects (i.e., rapid twitching of voluntary muscles and eventually paralysis). Has very broad spectrum toxicity and is highly toxic to fish.

Formamidines

Inhibit the enzyme monoamine oxidase that degrades neurotransmitters causing an accumulation of these compounds; affected insects become quiescent and die. Used in the control of OP and carbamate-resistant pests.

Dinitrophenols

Act by uncoupling or inhibiting oxidative phosphorylation preventing the formation of adenosine triphosphate (ATP). All types have been withdrawn from use.

Organotins

Inhibit phosphorylation at the site of dinitrophenol uncoupling, preventing the formation of ATP. Used extensively against mites on fruit trees and formerly used as an antifouling agent and molluscacide; very toxic to aquatic life.

Pyrethroids

Acts by keeping open the sodium channels in neuronal membranes affecting both the peripheral and central nervous systems causing a hyper-excitable state. Symptoms include tremors, incoordination, hyperactivity and paralysis. Effective against most agricultural insect pests; extremely toxic to fish.

Nicotinoids

Act on the central nervous system causing irreversible blockage of the postsynaptic nicotinergic acetylcholine receptors. Used in the control of sucking insects, soil insects, whiteflies, termites, turf insects and the Colorado potato beetle. Generally have low toxicity to mammals, birds and fish.

Spinosyns

Acts by disrupting binding of acetylcholine in nicotinic acetylcholine receptors at the postsynaptic cell. Effective against caterpillars, lepidopteran larvae, leaf miners, thrips and termites. Regarded for its high level of specificity.

Pyrazoles

Inhibits mitochondrial electron transport at the NADH-CoQ reductase site leading to disruption of ATP formation. Effective against psylla, aphids, whitefly and thrips. Results of testing on one type (fipronil) indicate no effects on the clams, oysters or fish, with marginal effects on shrimp.

Pyridazinones

Interrupt mitochondrial electron transport at Site 1; mainly used as a miticide; display toxicity to aquatic arthropods and fish.

Quinazolines

Acts on the larval stages of most insect by inhibiting or blocking the synthesis of chitin in the exoskeleton. Developing larvae exhibit rupture of the malformed cuticle or death by starvation; not registered in U.S.

Botanicals

Depending upon the type can have various effects: 
Pyrethrum – affects both the central and peripheral nervous systems, stimulating nerve cells to produce repetitive discharges and eventually leading to paralysis. Commonly used to control lice. 
Nicotine – mimics acetylcholine (Ach) in the central nervous system ganglia, causing twitching, convulsions and death. Used most to control aphids and caterpillars.
Rotenone – acts as a respiratory enzyme inhibitor. Used as a piscicide that kills all fish at doses non-toxic to fish food organisms.
Limonene – affects the sensory nerves of the peripheral nervous system. Used to control fleas, lice, mites and ticks, while remaining virtually non-toxic to warm-blooded animals and only slightly toxic to fish.
​Neem – reduces feeding and disrupts molting by inhibiting biosynthesis or metabolism of ecdysone, the juvenile molting hormone. Commonly used against moth and butterfly larvae.

Synergists/Activators

Inhibit cytochrome P-450 dependent polysubstrate monooxygenases (PSMOs) preventing the degradation of toxicants, enhancing the activity of insecticides when used in concert; synergists and activators are not in themselves considered toxic or insecticidal.

Antibiotics

Act by blocking the neurotransmitter GABA at the neuromuscular junction; feeding and egg laying stop shortly after exposure while death may take several days. Most promising use of these materials is the control of spider mites, leafminers and other difficult to control greenhouse pests. 

Fumigants

Act as narcotics that lodge in lipid-containing tissues inducing narcosis, sleep or unconsciousness; pest affected depends on particular compound.

Inorganics

Mode of action is dependent upon type of inorganic: may uncouple oxidative phosphorylation (arsenicals), inhibit enzymes involved in energy production, or act as desiccants. Pest group depends on compound (e.g., sulfur for mites, boric acid for cockroaches).  

Biorational

Grouped as biochemicals (hormones, enzymes, pheromones natural agents such as growth regulators) or microbials (viruses, bacteria, fungi, protozoa and nematodes). Act as either attractants, growth regulators or endotoxins; known for very low toxicity to non-target species.

Benzoylureas

Act as insect growth regulators by interfering with chitin synthesis. Greatest value is in the control of caterpillars and beetle larvae but is also registered for gypsy moth and mushroom fly. Some types are known for their impacts on invertebrates (reduced emergent species) and early life stages of sunfish (reduced weight) (Boyle et al. 1996).