What are Pesticides?
Introduction
A pesticide is defined as a substance or mixture of substances intended for destroying, repelling or mitigating any pest.
A pest is any living thing that exists where it is not wanted. Ideally, a pesticide should control a pest but not be detrimental to humans or other non-target organisms in the environment.
The following is a brief glossary of pesticides used in the pest control industry:
| Pesticide | Used Against |
| Acaricide (Miticide) | Mites |
| Avicide | Birds |
| Fungicide | Fungi |
| Herbicide | Weeds |
| Insecticides | Insects and related animals such as spiders, millipedes and centipedes |
| Molluscicides | Snails and slugs |
| Nematicides | Nematodes |
| Rodenticides | Rats, mice or other rodents |
How Insecticides Enter the Insect Body
Insecticides enter the insect body by three common ways; by contact, as stomach poisons or as fumigants. Many pesticides may enter the body by more than one of these possible routes.
Contact Insecticides
Insecticides in this class kill pests by contacting and entering their bodies either directly through the insect integument (skin) into the blood or by entering the respiratory system through the spiracles (air valves along the side of an insect's body which control gas exchange). These materials may be applied directly to the insect body or as a residue on plant or animal surfaces, habitations or other places frequented by insects. In cases where residues are used, pests usually contact the pesticide through their tarsi (feet). Generally speaking, coarse sprays or dusts are a more effective means of applying contact insecticides than are mists or fogs. Most of the synthetic organic compounds act as contact insecticide, although many also confer stomach and fumigant activity.
Stomach Poisons
Stomach poisons must be swallowed in order to cause death. They may be formulated as liquids, dusts, pastes, granules or baits. In the case of liquids and dusts, the pesticide is usually applied to some substance on which the animal will chew or walk through. Pastes, bait and granules may be formulated with a feeding attractant which is consumed by the pest. Inorganic and botanical insecticides in general are predominantly stomach poisons. Some synthetic organic insecticides may also act in this capacity.
Fumigant Pesticides
Gaseous poisons used to kill pests are called fumigants. Their applications are usually limited to materials, structures or organisms that can be or are enclosed in a tight enclosure. There are many fumigants, some distinctly odorless, while others are used in conjunction with odorless fumigants as a warning agent because of their odor.
Many can be used safely about food products and most are very stable at stipulated temperatures. Some combine with commodities to produce corrosion or undesirable gases. When properly used, a fumigant is non-flammable and unlike any other forms of pesticides, kills all the developmental stages of an animal. In the case of insects, this includes the egg, larvae, pupae, and adults. When a fumigant reaches the appropriate concentration, it will kill pests quicker than any other pesticide.
Miscellaneous Pesticides
This group includes pesticides which may enter the body through any one or more of the previously mentioned means, but have some specialized mode of action or means of application.
Systemic Insecticides
Systemic insecticides act mainly as stomach poisons. However these chemicals are typically applied to one area of a plant or animal and are translocated to another area. In the case of plants, systemics are typically applied to the roots or stems of a plant and move through the vascular system to the leaves. Examples are Systox, Thimet and Disyston.
Desiccant Dusts
When applied to an insect, these materials absorb or abrade off the outer waxy layer of the insect's cuticle, causing the loss of body fluids and death by dehydration. The common desiccating dusts used by pest control operators are silica aerogel and boric acid.
Chemosterilants
There are chemicals which cause sexual sterility in either the male or female insect or animal. Chemosterilants have not yet been used on a commercial basis.
Pheromones
These are chemicals which may be of potential use in preventing insect mating when used to saturate the habitat.
Antimetabolites
These are chemicals which interfere with the normal metabolic or physiological processes of animals.
Pesticide Groups
Pesticide classification or grouping may be based on any of several criteria. One of the most common means of classifying a pesticide is on the basis of similarities in chemical structure. Based on this mode of classification, there are 3 classes of pesticides commonly used in the structural pest control industry, the inorganic, botanical, and synthetic organic insecticides.
Inorganic Pesticides
Inorganic pesticides are typically derived from minerals or chemical compounds that occur as deposits in nature. Most of these compounds are quite stable and tend to accumulate in the environment. Some act as stomach poisons (borates and boric acid). Others are considered sorptive dusts (silica aerogel, diatomaceous earth) that absorb the waxy layer from the cuticle of pests. Many of the inorganic pesticides are relatively expensive and are only moderately effective in controlling insects and other pests. Common inorganic pesticides are silica aerogel, boric acid, borates, diatomaceous earth, cryolite, copper, and sulfur.
Botanicals
The botanical pesticides are extracted from various parts (stems, seeds, roots, flower heads) of different plant species. Botanical insecticides usually have a short residual activity and do not accumulate in the environment or in fatty tissues of warm blooded animals. Many botanical pesticides act as stomach poisons, although pyrethrins act mainly as a contact poison. Common examples of botanical pesticides are pyrethrins, sabidilla, rotenone, nicotine, ryania, neem, and limonene.
Synthetic Organic Insecticides
Synthetic organic insecticides do not naturally occur in the environment, but are synthesized by man. Since all these compounds have carbon and hydrogen atoms as the basis of their molecule (as do living plants and animals), they are referred to as organic compounds. The four basic types of synthetic organic insecticides are the chlorinated hydrocarbons, organophosphates, carbamates, and pyrethroids.
Chlorinated Hydrocarbons
This large group of insecticides varies considerably in toxicity to mammals. Most are only moderately toxic, however, a few are very toxic to mammals. The use of these materials has been severely criticized for their effect on the environment. Most chlorinated hydrocarbons are very stable and do not readily decompose in the environment. Most of these insecticides accumulate in the environment and in fatty tissues of birds and mammals. The use of most chlorinated hydrocarbons has been prohibited in the U.S.. Examples of the chlorinated hydrocarbons are DDT, BHC, dieldrin, chlordane, aldrin, endrin, heptachlor and methoxychlor.
Organophosphates
The organophosphates are an extremely large and diverse group of insecticides. Their toxicity to mammals range from extremely toxic to some of the least toxic pesticides known. Most organophosphoates are not persistent and will break down to non-toxic materials in one to 30 days, depending on the compound. Organophosphates do not accumulate in fatty materials and do not accumulate in food chains. These compounds act mainly as contact insecticides although they may also act as stomach poisons and fumigants. Common organophosphates are malathion, chlorpyrifos (Dursban), diazinon, dichlorvos (Vapona), acephate (Orthene), and propetamphos (Safrotin).
Carbamates
The carbamate compounds are also a large group of insecticides. As a rule, these compounds are slightly more persistent in the environment than the organophorphrous compounds, but do not accumulate in the environment or fatty tissues of mammals. Most carbamates are only moderately toxic to mammals. They mainly act as contact insecticides with some stomach activity. Common carbamate insecticides are carbaryl (Sevin) and propoxur (Baygon).
Insect Growth Regulators
Insect growth regulators are chemicals that affect the ability of insects to growth and mature normally. They are based on and often mimic the growth hormones that occur naturally within the insect's body. Because mammals do not molt like insects do, most insect growth regulators are not very toxic to man and domestic animals. Common insect growth regulators are methoprene (Precor), hydroprene (Gentrol, Gencor), fenoxycarb (Torus), and hexaflumuron (Sentricon)
Microbial Pesticides
Microbial pesticides are formulated disease organisms of pests, many of which are grown in large quantities in manufacturing plants. Some of the microorganisms available for pest control are bacteria, fungi, and nematodes. Some of the bacterial pesticides available are Bacillus thuringiensis variety kurstaki (Thuricide, Javelin) for control of caterpillars and Bacillus thuringiensis variety israelensis (Teknar, Vectobac) for control of mosquitoes. Some of the fungi available for pest control are Metarhyzium (Biopath) for control of cockroaches. Some of the nematodes available for pest control are Steinernema feltiae (Vector) for flea control.
Authors:
Philip G. Koehler, University of Florida
Robert A. Belmont, Florida Pest Control Association
This file is part of the UF/IFAS Basic Pesticide Training manual (SM-59) which is intended to provide intermediate training to pest control operators. The manual was adapted from a larger manual, Applying Pesticides Properly, which was developed by Ohio State University in cooperation with the Cooperative Extension Service, U.S. Department of Agriculture, and the Office of Pesticide Programs, U.S. Environmental Protection Agency.
Published: March, 1998
