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School IPM
University of Florida

Back to Pesticides

How Insecticides Enter the Insect Body

Miscellaneous Pesticides

Pesticide Groups

What are Pesticides?

A pesticide is defined as a substance or mixture of substances intended for destroying,

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

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

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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.

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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,

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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

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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

© University of Florida, Gainesville, FL

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