1. Insecticides Stephen J. Toth, Jr. Wayne G. Buhler
Department of Entomology Department of Horticultural Science
North Carolina State University North Carolina State University
Photograph by Scott Bauer

2. Insects and Mites 99% of species are of minor importance
Beneficial insects and mites are small group which include honey bees, lady beetles, parasitic wasps, and predaceous mites
Destructive insects and mites represent the smallest but most notable group
Photographs by Steve Bambara and Jack Bacheler.

3. History of Insecticide Use
Greek philosopher Homer reported the use of sulfur for fumigation and other pest control uses (1000 B.C.)
Pliny the Elder reported pest control practices from Greek literature (70 A.D.); included use of pepper and tobacco extracts, soapy water, vinegar, turpentine, fish oil, brine, lye, etc.

4. History of Insecticide Use
As recently as the 1940s, insecticides limited to the arsenicals, petroleum oils, nicotine, pyrethrum, rotenone, sulfur, hydrogen cyanide gas and cryolite
Synthetic organic insecticides introduced after World War II
National Agriculture Library

5. The Criteria for Judging Insecticide Effectiveness
Controls insects
Cost effective
Environmentally safe
Can be used safely
Tim McCabe

6. Mode of Action of Insecticides
Nerve poisons (axonic and synaptic)
Metabolic inhibitors
Muscle poisons
Alkylating agents
Physical toxicants
Cytolytic (cellular) toxins
USDA/ARS

7. Mode of Action of Insecticides Nerve Poisons
Axonic poisons: effect electronic transmission of nerve impulses along nerve axon; cause repetitive discharges of nerves that eventually results in paralysis; examples include DDT, pyrethrum and synthetic pyrethroids
Synaptic poisons: effect electronic transmission (chemical) of nerve impulse across junction between nerve cells (synapses); cause repetitive discharges of nerves that results in paralysis; examples include organochlorines, organphosphates, carbamates and nicotine

8. Mode of Action of Insecticides
Metabolic inhibitors: effect electron transport chain; examples are rotenone (slows heartbeat, depresses respiration and oxygen consumption, and causes paralysis and death) and arsenicals (inhibit respiratory enzymes)
Muscle poisons: have a direct action on muscle tissue; examples are ryania and sabadilla which increases oxygen consumption, followed by paralysis and death
Alkylating agents: react directly with chromosomes and enzymes in cells; examples are fumigants such as methyl bromide and ethylene dibromide

9. Mode of Action of Insecticides
Physical toxicants: mechanically blocks a physiological process; examples are oil (blocks respiratory openings in insects) and boric acid and silica gel (effects insect cuticle causing dehydration and death)
Cytolytic (cellular) toxins: cause cells to rupture and disintegrate; example is Bacillus thuringiensis which is ingested by insects and disrupts cells in the gut (causing paralysis of gut and cessation of feeding)

10. Routes of Exposure to Insecticides
Stomach poisons: insecticide must be ingested by the insect for toxic effect
Contact poisons: the insect must come into contact with insecticide for toxic effect
Scott Bauer

11. Classes of Insecticides: Inorganics
Inorganic insecticides do not contain carbon
Usually white and crystalline, resembling salts
Stable chemicals (persistent), do not evaporate and are frequently soluble in water
Sulfur: stomach poison; oldest known insecticide; controls mites, thrips, scale insects and caterpillars
Arsenicals: stomach poisons; very useful to agriculture from 1930 to 1956; include Paris green, lead arsenate and calcium arsenate
Others: cryolite (fluorine), boric acid and silica gels

12. Classes of Insecticides: Botanicals
Botanical insecticides are toxicants derived from plants
Flowers, leaves and roots are finely ground and used, or toxic ingredients of plants are extracted and used alone or in mixture; expensive; low toxicity to mammals
Used for centuries;
maximum use in U. S. in the 1960s
Nicotine: tobacco extracts, nicotine sulfate; nicotine is a nerve poison (mimics acetylcholine at nerve synapse)
Ken Hammond

13. . Rotenone: roots of Derris or cube plants;
rotenone is both contact and stomach poison; used for control of many insects and fish
Pyrethrum: extracted from flower of chrysanthemum;
nerve poison that paralyzes insects quickly (“knock down” effect);
used in household sprays and aerosols, and on many vegetables, fruits and ornamental plants
Others: Ryania (roots of shrub), Limonene (citrus peels), Sabadilla (seeds of lily) and Neem (oil extracts of neem tree seeds)

14. Classes of Insecticides: Organochlorines
Insecticides that contain carbon (organo-), chlorine and hydrogen; also known as chlorinated hydrocarbons
Highly persistent and bioaccumulate in environment
DDT: nerve poison (effects axon); more than 4 billion pounds used in agriculture and for public health; very inexpensive to produce (22 cents per pound); DDT’s persistence in the environment resulted in ban of its use in U. S. in 1973

15. . Lindane: gamma isomer of benzenehexachloride;
nerve poison that resembles DDT; limited uses remain
Cyclodienes: includes chlordane, aldrin, dieldrin and heptachlor;
extremely persistent insecticides and stable in the soil; used in soil to control termites and soil insect pests of agriculture; uses cancelled ( )
Toxaphene: a polychloroterpene;
once used on cotton

16. Classes of Insecticides: OrganoPhosphates
Insecticides that contain Phosphorus
Distinctive features are their acute toxicity to vertebrate animals and chemical instability (less persistent in the environment than organochlorines); related to nerve gases
Nerve poisons that inhibit acetylcholinesterase at nerve synapses; cause rapid twitching of muscles and paralysis
Examples include Malathion, chlorpyrifos (Dursban), diazinon and methyl parathion

17. Classes of Insecticides: Carbamates
Insecticides that are derivatives of carbamic acid
Distinctive features are their low toxicity to mammals (exception is aldicarb) and broad spectrum of insect control (used widely for lawn and garden insects)
Nerve poisons that inhibit acetylcholinesterase at nerve synapses; causes rapid twitching of muscles and paralysis
Examples are carbaryl (Sevin) and aldicarb (Temik)

18. Classes of Insecticides: Pyrethroids
Synthetic insecticides related to pyrethrum (botanical)
Pyrethroids are much more stable in sunlight (persistent) than pyrethrum and effective against insects at very low application rates (0.1 pound per acre)
Nerve poisons that effect nerve axon
causes repetitive discharges of nerves which results in eventual paralysis
Examples are allethrin and permethrin

19. Classes of Insecticides: Biorationals
Natural or synthetic substances specific for target pest(s), but have no adverse effect on humans or environment
Insect pheromones:
Sex pheromones used for male trapping,
monitoring, detection and
mating disruption;
example is gossyplure (pink bollworm)
Jack Bacheler

20. Classes of Insecticides: Biorationals
Insect growth regulators:
disrupt the growth and development of immature insects into adults; insect mortality is typically slow; examples are methoprene and fenoxycarb (Logic)
Microbials:
bacteria (Bacillus thuringiensis), viruses, fungi, protozoa and nematodes that are isolated, cultured and mass-produced for use as insecticides
Scott Bauer

21. Classes of Insecticides: New Chemicals
Nicotinoids: action similar to nicotine; example is imidacloprid (Gaucho)
Spinosyns: fermentation product of soil-inhabiting microorganisms; example is spinosid (Tracer)
Pyrrole: chlorfenapyr (Pirate)
Phenylpyrazole: fipronil (Frontline)

22. References
Ware, G. W. An Introduction to Insecticides. 3rd edition. Radcliffe’s IPM World Textbook. (
Ware, G. W The Pesticide Book. 4th edition. Thomson Publications, Fresno, California. pp