TECHNICAL PAPER # 27
UNDERSTANDING INSECT PESTS
AND THEIR CONTROL
Harold R. Willson
Dr. Ernest C. Bay
1600 Wilson Boulevard, Suite 500
Arlington, Virginia 22209 USA
703/276-1800 . Fax: 703/243-1865
Understanding Insect Pests and Their Control
[C]1985, Volunteers in Technical
This paper is one of a series published by Volunteers in
Assistance to provide an introduction to specific
technologies of interest to people in developing countries.
The papers are intended to be used as guidelines to help
people choose technologies that are suitable to their
They are not intended to provide construction or
details. People are
urged to contact VITA or a similar organization
for further information and technical assistance if they
find that a particular technology seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on a
Some 500 volunteers were involved in the production
of the first 100 titles issued, contributing approximately
5,000 hours of their time.
VITA staff included Maria Giannuzzi
as editor, Julie Berman handling typesetting and layout, and
Margaret Crouch as project manager.
The author of this paper, VITA Volunteer Harold R. Willson,
extension entomologist and integrated pest management
with the department of entomology, Ohio State
former Peace Corps Volunteer in India, Dr. Willson has
many overseas consultancies concerned with pest management
entomology, and is widely published in these fields.
of this paper are also VITA Volunteers.
Dr. Ernest C. Bay is
superintendent and professor of entomology for the
State University Western Washington Research and Extension
He is a specialist in the biological control of mosquitoes
and has consulted for the World Health Organization and VITA
Nicaragua, the Far East, Africa, and Haiti.
Kenneth Haines worked
in Ghana for several years where he supervised pest, control
as one of his duties as an agricultural extension
R. Narasimhan is with the Asian Pacific American Chamber of
VITA is a private, nonprofit organization that supports
working on technical problems in developing countries.
information and assistance aimed at helping individuals and
groups to select and implement technologies appropriate to
maintains an international Inquiry Service, a
specialized documentation center, and a computerized roster
volunteer technical consultants; manages long-term field
and publishes a variety of technical manuals and papers.
UNDERSTANDING INSECT PESTS AND THEIR
VITA Volunteer Harold R. Willson
Insect control is the effort made to protect crops, animals,
other targets of insect attack from unacceptable injury or
If destructive insect populations are allowed to cause
damage or injury to their target host, economic loss or a
decline in human health may result.
Destructive insects threaten the value of most food crops
before and after harvest.
In addition, insect pests can destroy
structures and cause direct injury to animals including
However, not all insects are destructive.
Some provide direct
economic benefit by producing products such as honey or
others naturally control harmful insect pests.
And of vital
importance is the role of insects in pollinating flowering
A population of a destructive pest and its target host (a
livestock, etc.) are part of a complex system that includes
other organisms living in a given physical environment or
Elements of a natural system, such as a crop, are in a
state of balance with one organism affecting the other.
occur when the natural balance between destructive and
insects is upset.
Corrective action is then required to control
the problem or prevent similar pest problems in the future.
II. METHODS OF INSECT CONTROL
Applied control includes a whole range of practices that
necessary when natural control factors fail to work
Important methods of applied control are:
legal control; and
In discussing each method, note that only general
be given since much depends on the type of insect pest, its
habits, and the kind of damage it causes.
Also important are the
nature and condition of the target host to be treated,
conditions, application equipment, and the method of
For information to meet specific needs, consult an
organization in your area.
The use of chemicals--generally referred to as
become the most common approach to dealing with insect problems.
An insecticide may be used as either a preventative or
treatment. In the
case of preventative treatment, it is assumed
that the probability of an insect becoming a problem is
Action is taken on the assumption that preventative treatment
more economical or effective than taking corrective action
the fact. However,
many insect pests are best controlled after
their numbers are so high that they might become a threat to
For crops the decision as to when to take corrective action
best based on an 'economic injury level' previously
for the host and its insect pest.
This involves the judgement of
the extent to which a particular pest population can be
to grow before an insecticide must be applied to prevent
crop loss. The
economic injury onset is determined by monitoring
the insect pest population in relation to its natural
weather, and host condition.
The timing of insecticide application can significantly
the potential for crop contamination.
The best times to apply
insecticides, especially if they are sprayed, are in the
morning or early evening hours when the air is still.
should never be sprayed in wind or when heavy rains--are
insecticides are applied early in the growing
season; but since this usually coincides with the rainy
season, the runoff merely carries the insecticides
possible, insecticides should be applied after crops have
emerged, later in the season, or even after the season to
fields for the next season.
People who use an insecticide to control a pest problem must
warned of the possible harmful effects it may have on the
beneficial insects (e.g., pollinators such as bees), or
the person who applies it.
Safety precautions and directions for
its use should be followed carefully.
Failure to take safety
precautions and to handle insecticides carefully may result
illness or death or contamination of water and food.
Continuous use of insecticides can destroy beneficial soil
and reduce soil fertility.
Some soil microorganisms
kill insect pests.
Overuse and misuse of insecticides can interfere
with the microorganism's ability to kill such pests.
this happens, pest problems can actually worsen: the pest
develop resistance to the insecticide, and since natural
have been wiped out, the pest populations can be virtually
at least for a time.
Remember that many insecticides kill not only target species
other harmless or beneficial organisms such as honeybees,
parasites, or predatory insects.
In many instances, the use of
insecticides to control one insect destroys the controlling
natural enemies of other species, allowing these to become
If you need to use insecticides, check with local farmers or
extension agency personnel to see what are the possible
of using them. Also,
look into alternative control measures that
may meet your needs without harmful effects.
Biological control involves using an insect's own natural
or enemies to control it.
Some of these controls are the
result of modern scientific research.
Very few biological controls are as readily available and
for controlling insect pests as insecticides.
These are almost
exclusively disease organisms, particularly Bacillus
which is effective against many Lepidopterous larvae and
Bacillus thuringieusis Israelensis, which is useful for some
Also, milky spore disease has long been marketed
for Japanese beetle control in the United States.
A few insect predators and parasites, including lacewing
(Chrysopa), ladybird beetles (Coccinellidae) and
species are sometimes marketed but their successful use
a professional understanding of the elements in the
where they are used.
More often these species are marketed more
for their ease of production then for their
notable exception is the mosquito fish Gambusia affinis,
preys on some pool dwelling mosquito larvae.
Many sites, however,
are not suitable for mosquito control by Gambusia.
must be taken that the fish does not become permanently
where it will eliminate other desired fish by competition.
The introduction of natural enemies to control imported
pests has proven to be the most effective biological
This usually requires the resources of government agencies,
research, and years of work.
Where it is successful as
with the classic case of the Vedalia beetle in the control
cottony cushion scale of citrus, it requires no further
of the natural enemy.
It simply requires the observance of
good agronomic and ecological practices to ensure the mutual
survival of prey and predator at acceptable pest levels.
Other types of biological control include release of
males, sterile hybrids, pheromones for attracting or
populations, and other innovative techniques.
These have been
used with varying success.
These practices usually require institutional
The use of chemical repellents is another method of
insect pests. For
example, chemicals that function as repellents
to household pests such as cockroaches can be used alone or
conjunction with an integrated control program to prevent
accumulation and reinfestation of cockroaches.
In cases where
immediate relief from, say, biting mosquitoes is needed but
control measures are impractical, repellents placed directly
the skin or sprayed on a piece of clothing can be very
Repellent-treated mesh jackets are effective for longer
In some situations, the term biological control also refers
the presence of native beneficial insects that are natural
of problem pests. It
is when natural control fails that
other controls are necessary.
This is the basis of pest management
and integrated control.
It is important to be aware of the
natural enemies of insect pests and to use those
that are least destructive to them.
As mentioned earlier, the
destruction or disturbance of natural control by some
can cause other insects previously under natural control to
assume pest status.
Manipulation of beneficial insects to control problem pests
requires extensive study and a long-term effort.
awareness of naturally present beneficial insects and the
chemicals least destructive to these insects may prevent new
Biological control methods have worked well in some
applications but may or may not work in other
should be considered as alternatives that may be used alone
combination with other pest control practices.
Many insect pest problems can be prevented by adopting crop
culture practices that adversely affect the development of
pests. For example,
rotation of certain crops can prevent
development of a given pest population that requires the
of the host crop over more than one growing season.
weed control often reduces the probability of some pests
a crop. The use of
cultural insect controls may or may not
provide an economical alternative to chemical control
on the situation.
Cultural controls can also be used to alleviate forest pest
culture practices include removing high-risk
trees, promptly treating pest-infested trees, disposing of
residues, and promptly harvesting damaged trees.
In nurseries, cultural control practices include carefully
irrigation, improving soil fertility, and regulating
Proper timing between lifting, fallowing, and
planting can also be useful in reducing pest populations in
Regulatory action by a governmental agency may be advisable
insect pests pose a threat to society.
Examples of legal control
include isolating a pest-infested area to prevent insects
spreading to other areas or requiring farmers to adopt
controls to reduce the impact of a given pest over an area.
Environmental control involves changing the environment in
way as to destroy insect life.
Three environmental control
methods are discussed below.
Examples of some physical means of excluding
insect pests include properly designed machinery or
constructing airtight doors, screening windows, controlling
filtering air, segregating commodities (e.g., grain
subject to high pest infestation, rotating commodities in
facilities, and developing insect-resistant packaging.
Temperatures below 5[degrees]C (40[degrees]F) prevent insect
activity and temperatures much below 0[degree]C
(32[degrees]F) for an extended
period usually kill insects.
Also, temperatures above 38[degrees]C
(100[degrees]F) for long periods or 60[degrees]C
(140[degrees]F) for short periods are
Sanitation involves good housekeeping practices.
Although sanitation by itself does not usually prevent
insect infestation, it often enhances the effect of
should these be needed.
The regular removal of dirt, dust, and grease from household
objects helps to prevent infestation.
Rotating heavy pieces of
furniture is also important because household pests usually
in areas where cleaning is difficult rather than in the open
where thorough cleaning, light, and the movement of people
Cereals and foods high in protein are attractive to
pests. Take care in
kitchen cabinets and other storage areas not
to let these materials accumulate in cracks and
removing other food sources such as garbage also prevents
pests from breeding.
INTEGRATED PEST MANAGEMENT
Integrated pest management (IPM) is a comprehensive approach
uses available control methods in an ecologically and
Its objective is to optimize pest control
in terms of overall economic, social, and environmental
By using a combination of the insect pest control practices
described thus far, an effective IPM program can reduce
use and thus prevent the damage to the environment caused by
the continuous use of insecticides.
Also, it can provide alternate
controls should any one method fail.
To ensure that an IPM program is economical, an IPM
may recommend the use of low-cost insect control methods for
field that has a low cash value per acre.
Thus, an IPM program
aims to incorporate cost-effective control practices into a
pest management system.
<![if !supportEmptyParas]> <![endif]>
IPM specialists are also aware of the important role
parasites and predators play in reducing insect pest
In many vegetable production areas, trained IPM specialists
to reduce insecticide treatments by making full use of
recommend insecticide applications for insect pests
only when needed, thus hoping for the least harm to
IPM specialists are also trying to reduce the use of
chemicals and to manage target hosts in a manner less likely
contribute to pest problems.
In forestry, for example, the
amount of direct chemical control of forest pests has been
in recent years.
Biological control agents are often
used to replace conventional chemicals.
Before undertaking an integrated pest management program,
needs to (1) learn as much as possible about the life cycle
environmental requirements of the insect pest; (2) find out
where or when the pest is most susceptible to control; and
(3) determine the least ecologically harmful way or
of ways to control it.
III. DESIGNING THE SYSTEM RIGHT FOR YOU
Design of a pest management program for a given pest or
of pests, whether affecting a crop, livestock, or other
aspect of human welfare, depends on the availability of
the pest must be identified. Accurate
of a pest enables review of the pest's biology, population
activity, nature of damage to host, etc.
a survey of the site should be conducted to assess the
degree of the problem.
Such a survey will provide an idea of the
relative importance of the pest in regard to a particular
Selection of appropriate pest control measures will depend
on the type of insect and available control methods.
The easiest and most common method for controlling
insects is chemical control.
Before a decision is made to use an
insecticide, one should consider: (1) the economic
of the action, and (2) the environmental implications of the
action, including the safety of the applicator.
Specific questions that need to be addressed before applying
insecticides to control crop pests include:
Does the pest threat justify the investment
At what stage of the pest's development will
substantial injury to the crop?
Is the pest population still present to
treatment? If so, is it vulnerable to such
Do any parasites, predators, or diseases
might lead to
a decline in the pest population?
What effect will prevailing climatic factors
population or the host crop?
Does timing the application of an
insecticide have an
effect on the
ability of the insecticide to control the
What effect will an insecticide have on
insects in the
What is the distribution of the pest problem
all areas be
Has the application been calibrated recently
If insecticide use is warranted, which
and applied within the remaining pre-harvest
What is the effectiveness of available
Are the insecticides available in your area
for use? Have
you checked with local authorities to
see if there
are specific laws governing the use of
Have adequate precautions been taken to
insecticide poisoning during transport, storage,
application of insecticides? Are instructions
Could the insecticide suggested for use kill
soil microorganisms or beneficial insects?
Have you considered all pest management
Is it likely that erosion will carry
water bodies? If so, could such insecticides
fisheries and domestic water use?
Can a species-specific insecticide be used?
Is it possible to switch insecticides to
target species developing resistance to
Have you contacted local universities and
information on local pest species and
practices to be sure you have considered
alternatives to insecticides?
To answer the above questions, the decision maker needs
information on the status of the crop threatened by a pest
information includes (1) identification of the
pest problem and associated organisms; (2) knowledge of the
biology and population dynamics(*) of the pest
(*)The aggregate of processes that determine the size and
of any population.
(3) familiarity with the host crop's capability to withstand
injury; and (4) knowledge of the effectiveness of available
insecticides under prevailing environmental conditions.
The suitability of chemical controls for an insect pest
on the availability of insecticides registered for use on
site in question.
The effectiveness of a given insecticide on a
new pest problem should be evaluated to determine
treatment, rates, time of application, and impact on the
Deciding whether or not to use biological or natural
requires detailed knowledge of related organisms that may be
parasites or predators of the pest in question.
Use of cultural
methods to control a pest requires a thorough understanding
the pest under various cultural practices.
biological or cultural control methods often depends on
research and evaluation.
If effective chemical methods are
available to control an insect pest, efforts to develop a
that integrates biological and cultural controls with
controls should be made to minimize dependence on any single
Once an insect control program has been established, the
effectiveness must be monitored regularly, especially if
the program depends heavily on the use of insecticides.
biological or cultural control methods, once established,
tend to be long lasting.
In contrast, dependence on insecticides
often requires continued re-evaluation and development of
compounds to maintain adequate control of the pest.
This is due
to the ability of insect populations to develop resistance
chemicals over time.
The development of resistance by an insect
population to insecticides is most likely in situations
single insecticide is used extensively.
Thus, any effort to
minimize excessive use of chemical controls and incorporate
or cultural controls will enable more effective use of
Methods of insect control differ with each combination of
and affected site.
Insects pass through various stages and the
stage targeted for treatment may or may not be the damaging
in the life cycle of the pest.
The environment of the host site
also has a significant effect on the control method adopted.
Insect pests inhabit a diversity of environments ranging
aquatic to soil ecosystems, and each environment presents a
different set of ecological factors for consideration.
Information on insect control is available from a number of
agricultural institutions throughout the world having
Agricultural chemical industries often provide
extensive information on important pests.
on over a million insect species around the world, of which
a few thousand are considered destructive insects of
the most important step in dealing with an
insect problem is the collection of accurate observations in
field which form the basis for future decisions.
IV. LABOR REQUIREMENTS
Development or selection of a pest management program for a
pest problem requires the services of personnel with
experience in the field of applied entomology.
Such personnel may
be entomologists or specialists in the host commodity field
substantial training or experience in pest control.
Where new insect control methods must be developed, the
of research entomologists with training or research
a particular specialty may be required.
in a number of areas depending on the commodity, method of
or level of technology being developed.
study the response of insects to toxic substances in the
study various aspects of insects in regard to
Biological control specialists study the relationship
between pests and natural agents that may be implemented
Taxonomists are often necessary to accurately identify
Entomologists who develop and implement field
methods are often referred to as economic entomologists or
Such applied field entomologists often
specialize by commodity fields (e.g., field crops,
fruit, forestry, livestock, stored products, human health,
The institutional source for entomological expertise
both public and private agencies.
In the United States, expertise
in entomology is primarily based in a network of state
experiment stations operated by state universities having
In addition, research and regulatory entomologists
operate out of state and federal departments of agriculture.
Implementation of new technology is performed by extension
entomologists associated with agricultural colleges.
each state, entomology extension specialists work through
county extention agents to educate farmers and the public
new pest control technology and the safe and proper use
Private industry--especially the agricultural chemical
an important source of pest control expertise.
many cases, the level and extent of expertise within private
industry exceeds that available from public resources.
companies have personnel with specific responsibility in
either (1) research, (2) product development, (3) technical
or (4) sales and marketing.
The geographical areas served
by industry personnel vary with the scope of the market
However, all geographical areas of the world are serviced by
private network of pest control specialists.
In general, a close
working relationship exists between government and private
in the development and implementation of pest control
One of the most important sources of information for farmers
the local chemical dealer, who often has more contact with
farmers than do public development personnel or other pest
Provision of education programs on the safe
and proper use of pesticides for such local dealers or
is important if the local user of pesticides is to receive
Education of local chemical dealers or
merchants in the appropriate pest control technology depends
programs available from both public and private
Public personnel should realize that the local chemical
often the primary source of pest control information and
educational programs accordingly.
Potential customers should bear
in mind that the chemical dealer or merchant has a vested
in his products and thus may not be the best source of
information on controlling a pest problem.
Chemical marketing programs should stress that the proper
a chemical to achieve effective control depends on the level
expertise available from local dealers.
Education of local chemical
dealers and applicators often depends on the implementation
of an educational program leading to certification in the
use of chemical pesticides.
Such programs often emphasize pest
identification, pest population assessment and control, and
participation in such training programs is a
requirement for the sale, purchase, or use of toxic
then participation in the educational program is facilitated
improper use of pesticides may be prevented.
BIBLIOGRAPHY/SUGGESTED READING LIST
BOOKS AND REPORTS
Bellotti, Anthony, and van Schoonhoven, Aart.
Cassava Pests and
Control. Cali, Colombia: Centro
Borror, D.J., and DeLong, D.M.
An Introduction to the Study of
New York, New York: Holt, Rinehart and
Bull, David A. A
Growing Problem: Pesticides and the Third
Oxford, England: OXFAM, 1982.
Cheaney, Robert L., and Jennings, Peter R. Field Problems of
America. Cali, Colombia: Centro
Davison, R.H., and Lyon, W.F.
Insect Pasts of Farm, Garden, and
Edition. New York, New York: John Wiley, 1979.
Biological Control of Insect Pests and Weeds.
York, New York:
Herms, W.B., and James, M.T.
Medical Entomology. 5th Edition.
New York, New
York: MacMillian Co., 1961.
Medical Entomology--Arthropods and Human Disease.
Jones, F.G.W., and Jones, M.G.
Pests of Field Crops. 2nd
New York, New
York: Edward Arnold, 1974.
Lindblad, Carl, and Druben, Laurel.
Enemies of Stored Grain. Vol.
2: Small Farm
Grain Storage. Arlington, Virginia:
Lozano, J.C.; Belloti, A.; van Schoonhoven, A.; Howeler, R.;
Doll, J.; Howell,
D.; and Bates, T. Field Problems in
Cali, Colombia: Centro Internacional de
Metcalf, C.L.; Flint, W.P.; and Metcalf, R.L.
New York, New York: McGraw-Hill,
Metcalf, R.L., and Luckmann, W.H. Introduction to Insect
New York, New York: Wiley-Interscience,
Mortensen, Ernest, and Bullard, Ervin T.
"Insect Control." Handbook
of Tropical and
Subtropical Horticulture. Washington,
D.C.: U.S. Agency
for International Development, June 1970,
Munro, J.W. Pests of
Stored Products. New York, New York:
Schwartz, Howard F.; Galvez, Guillermo E.; van Schoonhoven,
Reinhardt H.; Graham, Peter H.; and Flor, Carlos.
Field Problems of
Beans in Latin America. Cali, Colombia:
Inernacional de Agricultura Tropical, 1978.
Smith, E.H., and Pimentel, D.
Pest Control Strategies.
Academic Press, 1978.
University of the Philippines.
"Major Insect Pests of Rice and
Control." Rice Production Manual. Quezon City, The
University of the Philippines, 1967, pp. 211-36.
Volunteers in Technical Assistance.
"Background for Planning:
Management." Environmentally Sound Small-Scale Agricultural
Arlington, Virginia: VITA, 1979, pp.
Bulletin of the Entomological Society of America (quarterly)
Annuals of the Entomological Society of America (bimonthly)
Journal of Economic Entomology (bimonthly)
Environmental Entomology (bimonthly)
Insecticide and Acaricide Tests (annual)
<![if !supportEmptyParas]> <![endif]>