There are more than 400 compounds registered for use in the United States as insecticides, representing a range of chemical structures, applications and toxicities to insects and the greater environment, according to George Ware, emeritus professor of entomology, University of Arizona, Tucson, Ariz. While some formulas are general-purpose insecticides, others have specified uses due to their composition – and several have been subject to bans or heavily regulated uses in the landscape.
Here is a list of some of the most popular insecticides – by chemical family – through recent times.
INORGANIC COMPOUNDS – This large class of carbon-less insecticides was the mainstay of both outdoor and indoor pest control from the mid-1800s to the mid-1900s. These materials, usually salt-like crystalline dusts, are highly stable, generally do not evaporate and therefore deliver very high residual presence in the environment – a trait that has ruined their commercial viability in more recent times. This category contains various chemical subtypes that act in a number of biological ways: sulfur-based formulas are a fumigant and general toxin and double as a fungicide; arsenicals, including copper arsenate, Paris green and lead arsenate, impede oxygen transport and coagulate necessary proteins; fluorides, sodium fluoride and cryolite, impede the production of iron, calcium and magnesium; and boric acids eat away at insects’ insides and absorb cuticle wax, effectively drying them out. Because of inorganics’ residual environmental toxicity, most of these compounds have fallen out of favor since World War II, with only a few – sodium fluoride, cryolite and some sulfur dusts – still bearing commercial landscape uses. Industries use some others, like boric acid, sodium borate and silica aerogels, primarily to treat pest-susceptible materials and as part of integrated indoor pest control programs.
OILS AND SOAPS – This class of insecticide works by coating and suffocating small insects and their eggs. Most effective on scaled species, aphids, whiteflies and certain mites, these contact insecticides are made either of water and petroleum-based emulsions or natural animal or vegetable oils.
BOTANICAL EXTRACTS – Plant extracts have been effective in killing and repelling insects since ancient times. Some of the more popular plant-derived insecticides include: nicotine, which can cause tremors and eventually death in insects, particularly soft-bodied species like caterpillars; rotenone, which inhibits oxygen transport in insects (highly toxic to fish); ryanodine, which renders muscles useless; and pyrethrum, a chrysanthemum extract that causes seizures in insects by poisoning their nervous systems with their own sodium content.
ORGANOCHLORINES – These carbon, hydrogen and chlorine compounds were the first synthetic organic insecticides developed. They proved to be highly effective insect nerve poisons, but were eventually banned for most commercial uses in the United States as they have an extended residual presence in the landscape and accumulate in the fatty deposits of animals that feed on treated plants and/or insects, poisoning ecological food chains. Among this class of insecticides are: methoxychlor; dicofol; Lindane, now used only as an occasional seed dressing or a prescription drug for human lice; and DDT, roundly acknowledged as the most useful insecticide developed. Today, only endosulfan and kelthane are still registered for agricultural uses.
ORGANOPHOSPHATES – German scientists first discovered these phosphorus-based compounds as a nicotine substitute, and the Nazi regime later embellished them in tremor-inducing nerve gas research. While researchers generally consider organophosphates the most toxic insecticide to vertebrates, they view the class as significantly safer than organochlorines because of their much faster biodegradability. This group includes general-purpose insecticides, including malathion, parathion and diazinon; the fumigant DDVP; and systemics dimethoate, disulfoton and ronnel, which make the plant, itself, lethally poisonous to insects.
CARBAMATES – First developed in the early 1950s, this family of insecticides is comparable to organophosphates in that they are highly biodegradable, have low animal fat solubility and are, therefore, less residually detrimental to animals and humans. Like organophosphates, these insecticides cause tremors and ultimately death in insects. They include compounds such as methomyl, carbofuran and carbaryl, the most popular. Others, including oxamyl, aldicarb and formetanate, are systemics.
PYRETHROIDS – Imitating the pyrethrum compound in chrysanthemums, these synthetic compounds are relatively safe to humans, but increase sodium transport in insects, causing catastrophic nervous discharges. This synthetic insecticide, with a residual effect of up to 10 days, has all but replaced natural pyrethrum, which breaks down rapidly in sunlight. Popular pyrethroids include permethrin, fenvalerate and acrinathrin.
ORGANOSULFURS AND ORGANOTINS – This small group of insecticides has low toxicity to insects, and is generally only effective in alleviating mites. Sulfur-based organosulfurs are particularly effective in destroying viable eggs, while tin-based organotins double as fungicides. The family includes aramite, tetradifon, cychexatin and hexakis.
FORAMIDINES – Another small group of compounds, these insecticides are effective in battling species that have developed a resistance to organophosphates and carbamates. Foramidines create an excessive buildup of the natural hormones norepinephrine and seratonin in insects, literally lulling them to sleep – for good.
AVERMECTINES – Within the past five years, chemists discovered this class of chemicals in the soil-dwelling fungus Streptomyces avermilitis. These insecticides induce paralysis by preventing the transmission of nerve impulses to muscles. The chemicals in this category – avermectin, abamectin and ivermectin – only affect insects, certain mites and certain types of plant-parasitic worms.
NITROGUANIDINES – With both topical and systemic insecticidal properties, this chemical category battles a wide variety of sucking insects like aphids, leafhoppers and whiteflies. The flagship compound in this class, imidacloprid, mimics nicotine, causing tremors and eventual death in insects.