insect pest control

Insect Pest Control

INSECTS are the most diverse group of animals onEarth. More than 900,000 insects have been

identified, and it is believed that millions morehave yet to be discovered. Approximately20,000 species of grasshoppers and120,000 types of flies are known toexist. Understanding insects and theirsignificant roles in agriculturalproduction is essential to cropproduction.

Objective:

� Describe insect pest management.

Key Terms:

�

Controlling Insect Pests

An insect is an animal that breathes air and has an exoskeleton, three body segments, three

pairs of legs, two sets of wings (in most cases), a pair of antennae, and compound eyes. Insects

E-unit: Insect Pest Control

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ametamorphic

antennae

antibiosis control

beneficial insect

biological control

chemical control

chitin

completemetamorphosis

contact insecticide

cultural control

exoskeleton

external feeding insects

genetic control

harmful insect

incompletemetamorphosis

insect

internal feeding insects

larvae

mechanical control

metamorphosis

mode of action

nonpreference control

nymphs

pest resurgence

pesticide resistance

pupa

respiratory insecticide

stomach insecticide

subterranean insects

tolerance control

viviparous

are in the Kingdom Animalia, Phylum Arthropoda, and the class Insecta. The Arthropoda phylum

includes animals with exoskeletons and segmented bodies.

Insects have an exoskeleton that composes the insect’s body wall. Made of chitin (a

hard, flexible carbohydrate), the exoskeleton provides protection and support for the insect.

Muscles and organs are attached to the inside wall of the exoskeleton.

The exoskeleton consists of a number of segments. Some segments are easy to see, while

others are fused tightly together and are difficult to see. These segments form the three major

body sections: head, thorax, and abdomen. The head contains the brain, mouthparts, and sen-

sory organs, including the eyes and antennae. The antennae are segmented appendages that

act as sensory organs. The thorax is the center section to which wings and legs are attached,

and the abdomen contains organs for food digestion, respiration, reproduction, and excretion.

Some insects are ametamorphic (without metamorphosis). The insect hatches from the

egg as a very small replica of the full-grown adult. Ametamorphic insects also can be vivipa-

rous (giving birth to live young with no egg stage) or parthenogenic (reproducing asexually).

INSECT DEVELOPMENT

Most insects reproduce sexually but differ in development from the young to the adult

stage. Insect stages of development are known as metamorphosis, and the changes from egg

to adult are distinct.

An incomplete metamorphosis has three stages of development: egg, nymph, and

adult. Eggs hatch into nymphs, which are immature forms that resemble the adult. A nymph

usually molts and loses its exoskeleton. Molting allows the insect to grow. After an insect


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ON THE JOB…

CAREER CONNECTION: Entomologist

An entomologist is a scientist who studies insects. Entomologists may study the classifica-

tion, life cycle, distribution, physiology, behavior, ecology, or population dynamics of insects.

They may specialize in the study and control of urban pests, forest pests, agricultural pests, or

veterinary pests. Some entomologists focus on beneficial insects like honey bees, silkworms,

ladybird beetles, and parasitic wasps.

Entomologists are trained to recognize pest problems. They determine the seriousness of the

pest problem and design programs to manage the pests without hurting the environment and

the people in the area.

Training requirements for entomologists depend on the type of work they perform. Prepara-

tion requires the study of biology, zoology, botany, ecology, and chemistry. A bachelor’s degree

is sufficient for some jobs, but a master’s or doctoral degree is generally required for basic

research or for jobs directing applied research. Entomologists find employment as researchers,

teachers, and consultants. They may work for private companies, universities, or government

agencies.

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molts, it grows a new and slightly larger exoskeleton. Nymphs experience this process several

times before reaching the adult stage.

A complete metamorphosis has four stages of development: egg, larvae, pupa, and

adult. Larvae are segmented, worm-like forms that often inflict considerable damage on

plants. After an active larva stage, a pupa is formed. The pupa is a resting stage before the

insect becomes an adult. Most pupae are surrounded by a cocoon or a protective case.

INSECT CLASSIFICATION

An insect is classified based on its metamorphosis type, its usefulness or harmfulness to

humans, and its feeding method.

Beneficial Versus Harmful

A beneficial insect takes part in activities that help humans provide for their needs. Ben-

eficial insects perform a number of valuable activities. For example, beneficial insects may be


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Egg

Egg

Egg

Larvae Pupae Adult

AdultNymphs

Incomplete Metamorphosis — Gradual Change

Complete Metamorphosis — Complete Change

No Metamorphosis — No Change

FIGURE 1. Some insects go through a complete metamorphosis, while others only experience a

gradual change.

predators or parasites of harmful

insects, destroy various weeds, or be

plant pollinators. Benefits might

include food for man and animals,

medicinal purposes, scavengers that

eat decaying organic matter, and

aesthetic value.

A harmful insect causes dam-

age to plants, animals, or property.

It injures or destroys what it attacks.

Harmful insects damage food, feed

crops, and ornamentals. These

insects also attack man and his

domestic animals, attack stored

products, transmit disease, and are a

general nuisance.

Feeding Habits

Insects can be classified accord-

ing to mouthparts, which deter-

mine how an insect feeds. Control

measures often are selected based

on the way insects feed. Insects may

have chewing, piercing and sucking,

sucking, or sponging mouthparts.

Insects with chewing mouth-

parts cut, tear, crush, and chew

leaves, stems, roots, flowers, and

fruit. Examples of insects with chewing mouthparts are Japanese beetles, grasshoppers, and the

larva of moths and butterflies. Holes in leaves, buds, flowers, or other plant parts indicate dam-

age by a chewing insect.

Insects with piercing and sucking mouthparts puncture plant tissues and suck the internal

fluids. Examples of insects with piercing and sucking mouthparts are aphids, scale insects, and

leafhoppers. Damage often appears as tiny spots.

Insects with sucking or siphoning mouthparts draw fluids (e.g., nectar) up the tubu-

lar-shaped mouthpart. For example, butterflies and moths have sucking mouthparts.

Some insects, such as houseflies, have sponging mouthparts. These insects coat a food with

saliva and sponge it up.

Damage caused by insects may affect photosynthesis through defoliation and damage fruits,

stems, and roots. Most plants can withstand low to moderate infestations, but heavy infesta-

tions can kill plants. Some insects also carry disease from one plant to another.

Different types of insects feed on different plant parts. External feeding insects chew

or suck from the plant exterior. They feed on the leaves, stems, buds, or fruit. Internal feed-


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FIGURE 2. The bee is one of nature’s plant pollinators.

FIGURE 3. These insect larvae have completely destroyed these two

tomatoes.

ing insects are chewing insects that cause damage to the inside of a plant. They feed internally

on plant tissues, and the damage may not be evident for several days or longer. Subterra-

nean insects are species in the soil that attack plant roots. In some cases, they may attack

root-type structures.

MANAGING INSECT POPULATIONS

Selecting and using the correct method of insect

management is important. Management measures are

expensive and have other effects, such as killing benefi-

cial insects. Therefore, proper pest identification is

essential. Measures are based on the species and the

way it feeds.

The damage by the pest should be at a level that

merits action. Minor damage may not justify using

pesticides. Some methods of pest management can be

dangerous to people, other living organisms, and the

environment.

Many different methods can be used to manage

insects. Most fall under the categories of biological,

cultural, mechanical, genetic, regulatory, and chemical.

Biological Control

Biological control is the use of living organisms

to reduce pest populations. These organisms are natu-


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Chewing Pierce-Sucking

Antenna

Eye

Clypeus

Mandible

Labrum

Maxilla

Palpae

FIGURE 4. Chewing and piercing-sucking insects have various mouthparts.

FIGURE 5. The phorid fly is used as a means of

biological control on fire ants. (Courtesy, ARS,

USDA)

ral enemies of pests. They attach, live in, or infect the pest host. Parasites, predators, and

pathogens are all used as biological controls.

Cultural Control

Cultural control is used to make the crop environment unsuitable for pests to feed, live,

or reproduce. It also is used to improve the health of the crop. Examples of cultural controls

include soil tillage, crop rotation, adjustment of harvest or planting dates, irrigation schemes,

variety selection, clean culture, and trap crops.

Mechanical Control

Mechanical control is used to physically remove or exclude pests. It includes hand

destruction in addition to the use of screens to keep out insects and traps to catch them.

Genetic Control

Genetic control of plant pests involves the use of a genetically modified organism

(GMO). Plant breeders are constantly working to develop varieties and hybrids that are resis-

tant to insects or tolerant of pest feeding. Genetic control of insects and mites can be accom-

plished by nonpreference control, antibiosis control, and tolerance control.

Nonpreference control allows plant breeders to alter the plant’s biochemistry or constit-

uents so a particular variety or hybrid is less palatable to the pest. If the taste, aroma, color, or

texture of the crop plant is undesirable to the pests, they move to a different variety or a differ-

ent host plant (e.g., another crop or a weed).

Antibiosis control is a group whereby the crop plant components have a harmful effect

on the growth or reproduction of the pest when it feeds on it.

Tolerance control allows the host plant not to suffer economic damage even though it

may be heavily infested with a pest.

Chemical Control

Chemical control is the use

of pesticides to reduce pest popu-

lations. However, pesticide

resistance (the ability of an

organism to tolerate a lethal level

of a pesticide) can occur. In some

cases, pest resurgence (a pest’s

ability to repopulate after control

measures have been eliminated or

reduced) might make additional

control methods necessary.


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FIGURE 6. Chemicals are being sprayed to combat potential pest problems.

(Courtesy, USDA)

TYPES OF INSECTICIDES

Pesticide families include carbamates, organochlorides, organophosphates, pyrethroids, and

biological insecticides.

Carbamate

Carbamate insecticides are moderate to very high in toxicity. Insecticides from this family

include aldicarb, carbaryl, carbofuran, methomyl, pirimicarb, and propoxur.

Organochloride

Organochloride insecticides are highly toxic. Insecticides from this group are very danger-

ous because they are absorbed by the fatty tissue of animals. The insecticides do not break

down for years. Because of this, the toxins accumulate in the body of animals and can flow

down the food chain. Insecticides from this family include DDT, dicofol, endosulfan, lindane,

and methoxychlor.

Organophosphate

Organophosphate insecticides have low to very high toxicity. Insecticides from this family

include acephate, azinphos-methyl, chlorpyrifos, diazinon, dichlorvos, dimethoate, fenthion,

malathion, and parathion.

Pyrethroid

Pyrethroid insecticides kill insects by disrupting their nervous systems. These are

nonpersistent and much less acutely toxic than organophosphates and carbamates. Pyrethrins

and pyrethrum are the most frequently used home and garden insecticides in the United

States. They are often used in indoor sprays, pet shampoos, and aerosol bombs to kill flying

and jumping insects.

Biological

Biological insecticides include plant toxins (e.g., caffeine, nicotine, pyrethrum, and

rotenone). Another example is a bacterial disease caused by Bacillus thuringiensis, which is effec-

tive on insect larvae and is considered environmentally friendly.

INSECTICIDE MODE OF ACTION

The various insecticides kill insects in different ways. The way in which a pesticide kills or

inactivates a pest is called mode of action. Some insecticides affect the nervous system. Oth-

ers affect water balance, oxygen metabolism, an insect’s molting or maturation process, or


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other aspects of physiology. The

mode of action of a number of the

newer insecticides is not yet fully

understood.

Organophosphates (e.g.,

Chlorpyrifos, diazinon, and mala-

thion) interfere with the trans-

mission of nerve impulses. Their

point of action is the synapse,

which is the tiny gap between one

nerve fiber and the next.

Organophosphate enzymes are

involved in this process. Exposure

symptoms are hyperactivity,

uncoordinated movements, trem-

ors, convulsions, or paralysis.

Carbamates inhibit the action of cholinesterase such as organophosphates. Hyperactivity,

uncoordinated movements, tremors, convulsions, or paralysis are a result. Carbaryl,

bendiocarb, and propoxur are examples of carbamates.

Pyrethroids, such as ermethrin, cypermethrin, fenvalerate, and cyfluthrin, were synthesized

by chemists who studied the structure of insecticidal pyrethrins. Pyrethroids last longer than

their natural counterparts. They disrupt the normal transmission of nerve impulses by affect-

ing the potassium or sodium ion channel in nerve cells.

Insect growth regulators are effective with immature insects because they cause an insect to

change into an adult or pupa when the insect is not physiologically ready. Methoprene and

pyriproxifen are examples of insect growth regulators.

Chlorinated hydrocarbons, including methoxychlor and dicofol, interfere with the normal

movement of potassium and sodium ions across nerve cell surfaces. As a result, normal nerve

cell functions are prevented.

Microbial insecticides consist of microorganisms that attack insects. To be effective, insects

must eat the virus-based insecticides. Inside the insect, the viruses multiply and the insect’s

cells burst and die. Bacillus thuringiensis also needs to be eaten by insects in order to work.

The bacteria attack the gut lining, invade the insect’s body, and multiply. Fungal insecticides

attack from the outside. The fungal spores land on the insect’s body, grow through the cuticle

and exoskeleton, and spread throughout the body.

Insecticidal soaps are usually composed of potassium salts of fatty acids. Insecticidal soaps

must contact the outer body covering of insects where they can penetrate and dissolve nearby

cells. As a result, cell fluids leak out and the cells collapse, which results in dehydration and

death.

Oils are used with mites, scale insects, and aphid eggs. The oil kills by smothering the pest.


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FIGURE 7. Because this insecticide affects an insect’s oxygen metabolism, it

is considered a fumigant. (Courtesy, USDA)

STOMACH, CONTACT, AND RESPIRATORY INSECTICIDES

Insecticides are classified by how they enter an insect’s body. Three general groups of insec-

ticides are contact, stomach, and respiratory.

Normally used with sucking

insects, contact insecticide is

absorbed through the skin or

exterior of an insect. The chemi-

cal must be applied directly on the

insect.

Most effective on chewing

insects, stomach insecticide is

effective when eaten. The chemi-

cal is applied to the plant parts,

which are eaten by the insect.

Used in enclosed places,

respiratory insecticide enters

the respiratory system of the

insect. It is commonly called a

fumigant.

Summary:

� An insect is an animal that breathes air and has an exoskeleton, three body seg-ments, three pairs of legs, two sets of wings (in most cases), a pair of antennae, andcompound eyes.

Insects go through stages of development known as metamorphosis. Incompletemetamorphosis has three stages of development: egg, nymph, and adult. Completemetamorphosis has four stages of development: egg, larvae, pupa, and adult.

Insects are classified by the kind of metamorphosis, whether they are beneficial orharmful, and the way they feed. Insect pests may be external feeding, internal feed-ing, or subterranean.

Different methods used to manage insects include biological, cultural, mechanical,genetic, regulatory, and chemical.

Pesticide families include carbamates, organochlorides, organophosphates,pyrethroids, and biological insecticides. The way in which a pesticide kills or inacti-vates a pest is called the mode of action. Three general groups of insecticides arecontact, stomach, and respiratory.


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FIGURE 8. This small area of land has been fumigated.

Checking Your Knowledge:

� 1. What is an insect?

2. How are insects classified?

3. How does incomplete metamorphosis compare to complete metamorphosis?

4. What are methods of managing insect pests?

5. How are insecticides classified?

Expanding Your Knowledge:

� Make an insect collection. Seek help from your teacher or from the Internet onhow to catch, kill, mount, and label insects for display. As you make the collectionand identify the insects, determine if they are beneficial or harmful insects.

Web Links:

� Entomology Image Gallery

http://www.ent.iastate.edu/imagegallery/

Field Crop Insects

http://www.uky.edu/Ag/Entomology/entfacts/effldcrp.htm

Insecticide

http://en.wikipedia.org/wiki/Insecticide

Integrated Pest Management

http://www.ipm.uiuc.edu/


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http://www.ent.iastate.edu/imagegallery/

http://www.uky.edu/Ag/Entomology/entfacts/effldcrp.htm

http://en.wikipedia.org/wiki/Insecticide

http://www.ipm.uiuc.edu/

insect pest control

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