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                         TECHNICAL PAPER # 65
                       UNDERSTANDING INTEGRATED
                            PEST MANAGEMENT
                            David Pimentel
                          Technical Reviewers
                               H. C. Cox
                             Michael Dover
                               Jon Myer
                              Ron Stanley
                           Allen Steinhauer
                             Published By
                   1600 Wilson Boulevard, Suite 500
                     Arlington, Virginia 22209 USA
                 Tel: 703/276-1800 . Fax: 703/243-1865
               Understanding Integrated Pest Management
                          ISBN: 9-86619-304-9
              [C]1989, Volunteers in Technical Assistance
This paper-is one of a series published by Volunteers in Technical
Assistance to provide an introduction to specific state-of-the-art
technologies of intrest to people in developing countries.
The papers are intended to be used as guidelines to help
people chooe technologies that are suitable to their situations.
They are not intended to provide construction or implementation
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 illustrated
almost entirely by VITA Volunteer technical experts on a purely
voluntary basis.  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 Patrice Matthews
handling typesetting and layout, and Margaret Crouch as project
The author of this paper, David Pimentel is a professor of Entomology
at Cornell University in Ithaca, New York.   It was reviewed
by H.C. Cox, a consultant in agriculture, Michael Dover,
an environmental consultant, Jon Myer, an engineer at the Hughes
Research Laboratories, Ron Stanley, who is employed by the
Environment Protection Agency in agricultural development, and
Allen Steinhauer, the Executive Director of Consortium for International
Crop Protection.
VITA is a private, nonprofit organization that supports people
working on technical problems in developing countries.   VITA
offers information and assistance aimed at helping individuals
and groups to select and implement technologies appropriate to
their situations.  VITA maintains an international Inquiry Service,
a specialized documentation center, and a computerized
roster of volunteer technical consultants; manages long-term
field proejcts; and published a variety of technical manuals and
                   by VITA Volunteer David Pimentel
When the new synthetic pesticides were first used on world crops
in 1945, some people believed that the `magic bullet' or ultimate
specific weapon for pest control had been discovered.   As a result,
ecological studies of pests--their life histories and
environment--declined and investigations of nonchemical control
were drastically reduced.  In the industrialized countries, pesticides
were the main method of pest control for nearly three
With pests destroying about one-third of all crops in the world
and the significant damage occurring in developing countries
[Reference 1), it is no wonder that many farmers felt desperate
enough to consider that pesticides were the only solution.  Certainly,
for a short time, there was widespread hope that losses
to pests could significantly be reduced by the use of pesticides.
In fact, heavy pesticide use did result in major reductions in
the damages by some pests for short periods, but no overall
reduction in losses from pests has occurred.   For example, since
1945, U.S. crop losses to pathogens and weeds have fluctuated but
have not declined.
Changes in Agriculture
Rather, surprisingly, U.S. crop losses due to insects have nearly
doubled (from 7 percent to about 13 percent) [6].   This has occurred
in spite of a more than 10-fold increase in the use of pesticides,
including insecticides.  Fortunately, in recent decades,
the impact of this loss has been offset effectively by increased
crop yields.  The increase has resulted from planting higher-yielding
varieties and using more fertilizers, other fossil-energy
inputs, and irrigation.  Similar changes in crop-growing
practices occurred throughout the world.
The significant increase in insect damage to U.S. crops can be
accounted for by some of the major changes in agricultural practice
since the 1940s.  These include the planting of crop varieties
that are susceptible to insect pests; destruction by pesticides
of such natural enemies of pests as beneficial insects
and mites; and increased use of fertilizers.   In the United States
as elsewhere, all of these changes required additional pesticide
treatments, for example in cotton, and led to the development of
pests resistant to pesticides.   Moreover, reducing crop rotation
and crop diversity and increasing the use of single crop varieties
(monoculture) resulted in the need for more insecticide
use, for example in maize.  Concurrently, the U.S. government
reduced tolerance levels for insects and insect parts in marketed
foods, and processors and retailers raised `cosmetic standards'
for more perfect fruits and vegetables.
Farmers removed less crop debris from their fields and orchards,
often to achieve the benefits of reduced water evaporation and
soil erosion.  However, the practice also often led to increased
pest problems.  For example, less attention is now given to the
destruction of infected fruit and crop residues (e.g., apples).
Reduced tillage, with more debris left on the land surface, has
become common.
The culturing of such crops as potatoes and broccoli has been
extended into new climatic regions and made them more susceptible
to insect attack.  In addition, the use of pesticides that alter
the physiology of crop plants has made some crops (maize, for
example) more susceptible to insect attack.
Costs of Pesticide Use
Pesticides have helped to control some posts.   However, their
heavy use has brought serious social consequences and extensive
changes in the environment.  Human poisonings by pesticides are
the highest price paid for intensive pesticide use.   Each year in
the world, an estimated 500,000 humans are poisoned by pesticides,
with 10,000 fatalities.
Another indirect cost of pesticides is the reduction in the
numbers of natural enemies of pests.   When this occurs, more
pesticide must be used to control the resulting pest outbreaks.
With cotton, for example, four to five additional sprays are
applied to compensate for the destruction of natural enemies of
the cotton bollworm and budworm.   Annually, the cost of these
added sprays needed to offset the loss of natural enemies on U.S.
crops amounts to an estimated US $153 million.
High pesticide use often results in pests that develop resistance
to the chemicals.  To cope with this, growers apply higher doses,
additional sprays, and more powerful pesticides.   The estimated
annual cost of coping with increased pest resistance to insecticides
for U.S. crops is about $134 million and for the world,
$600 million.  Yet, increased pesticide use encourages further
resistance and amplifies environmental problems associated with
their use.  Other harmful effects of pesticides include the destruction
of honey bees, reduced pollination, fish kills, and the
unintentional killing of crops (herbicides, etc.). Overall, the
environmental and social costs annually total at least $1 billion
world wide.
Given this background to the problems associated with the `single
factor' approach to pest control with pesticides, several scientists
suggested the need for an approach that considered many
environmental factors, even if their consideration led to controlling
just one factor in the environment.   Studies of apple-pest
control in Canada in the early 1960s and of malaria-carrying
mosquitoes in the Tennessee Valley (USA) in the 1930s were the
forerunners of integrated pest management, confirming the need
for an interdisciplinary systems approach to pest control.  This
was an approach that took into account the interactions among
pest species and with plant hosts, as well as the life histories
and environments of both.  (Nonchemical controls had, of course,
been used with and without chemicals for many years.   Interest in
integrated pest management (IPM) has grown and has now become the
stated goal of most pest control operations in most countries.
This paper examines the complex nature of pest problems and
evaluates both chemical and nonchemical controls.   The objectives
of IPM are assessed, together with its current accomplishments
and its future as a pest-control strategy.   Although the paper
emphasizes agriculture, the concepts and strategies of IPM can
also be applied to forestry, the management of range and pasture
land, the control of insects that carry human and animal diseases,
and the control of such urban pests as rats and cockroaches.
The agricultural uses of IPM vary greatly with local conditions.
In addition to the general concepts in this paper, specific
information is available in most countries from international
agricultural centers and government research stations.
Integrated pest management is a technology for controlling agricultural
and other pests for the benefit of society as a whole.
In agriculture, pest-control strategies must consider not only
the pest in its total agricultural environment, but also the
surrounding environment and society that agriculture serves.
In developing strategies for an IPM program, reliable information
on the following is vital:
1.  The ecological basis of the pest problem.
2.  Factors in the agroecosystem that can be manipulated to make
    the overall environment unfavorable for weeds, insects, and
    plant pathogens while producing an optimal crop yield.
3.  A target level for reducing the post population, below
    which the degree of damage is acceptable.
4.  Pest and natural enemy population trends, based on careful
    monitoring, to determine if and when pesticide treatments are
5.  An analysis of the benefits and risks of the proposed IPM
    strategies for the farmer and society as a whole.
Knowledge of the ecological basis of the pest problem, discussed
in depth later, suggests ways to alter the crop environment to
reduce pest problems and losses.   Some nonchemical environmental
manipulations to control pests will also be discussed.
IPM is a first line of defense.  Not all pest problems, however,
can be solved by manipulating factors in the crop environment.
Thus, the second line of defense is the use of pesticides.  When
a pesticide is needed, it should be used, but in such a way as to
cause minimal damage to the natural enemies that also are important
controls of the major and potential pests.   This requires
extensive knowledge of the ecology of the pest as well as that of
beneficial natural enemy populations.   With adequate information
on beneficial and pest populations, a pest-control specialist can
determine which pesticide to use and when to apply it for maximal
The decision of when a pesticide should be applied will also
depend on the level of injury by the particular pest at which
there is a significant economic loss.   Determining `economic
injury levels' requires detailed knowledge of the following:
1.  Density of a pest.
2.  Densities of its parasites and predators.
3.  Temperature and moisture levels and their impact on the crop,
    pest, and the pest's natural enemies.
4.  Level of soil nutrients available to the crop.
5.  The growth characteristics of the particular crop
6.  Crop(s) grown on the land the previous year.
Of course, using a combination of nonchemical controls plus
keeping pesticide applications to a minimum has environmental
and public health advantages while at the same time being important
to the farmer.  First of all, reducing pesticide use reduces
crop production costs.  Second, and equally important, using a
combination of controls including pesticides reduces the chances
of the pests being able to overcome all of the control technologies.
This relates especially to overcoming the resistance to
the pest that the host plant has (`host-plant resistance') or can
develop  As a result, the useful life of both nonchemical and
pesticidal controls and their benefit to society could be extended.
Another important reason for using several control methods
is that the climatic and other environmental factors change
and may render one or more control factors less effective than
Although nonchemical controls offer fewer risks to the environment
than do pesticides, they are not without risks.   The final
and perhaps the most important step in developing successful IPM
strategies entails a careful benefit and risk analysis of the
technique, including measuring its environmental and social
costs.  This is essential if the control program is to provide
maximum benefits to agriculture and society as a whole.
IPM is a highly complex technology, even if the complex ecology
of pest groups in an agroecosystem is understood (see diagram in
Figure 1).  Furthermore, manipulating the numerous factors in an

uim1x6.gif (600x600)

agroecosystem to make the environment of a pest unfavorable while
maintaining a favorable environment for the crop is a major
challenge.  Selecting' and balancing nonchemical controls and
pesticides to use in combination is a difficult task.   The process
can be aided by carefully analyzing the benefits and risks of
an IPM program, taking environmental and other biological factors
into consideration as described above.
Although IPM has a complex basis, it sometimes uses only one
control technique; for example, in some situations well designed
and managed crop rotation can reduce the level of a pest population
to tolerable levels, and keep it there, without the use of
other types of control methods.
IPM uses combinations of nonchemical pest controls including
biological controls, host-plant resistance, cultural, and other
techniques.  The term "nonchemical control" refers to human activities
that manipulate the pest's environment, its ecological
relationships, or a combination of these [5, 6].   Again, it must
be emphasized that there are no instant, magical control measures,
whether they are pesticides or nonchemical controls.   Pest
populations must be managed in the context of the total agroecosystem (4).
Resistance of Host Plants
Many plants in nature have evolved to limit the feeding of pests
on them.  Through careful selection and breeding, genes can be
incorporated into a cultivated plant that confer resistance to
specific pests and thus provide effective control.   For example,
the Hessian fly, a serious pest of wheat, is effectively controlled
on a large portion of U.S. wheat cropland because the wheat
is bred for resistance to the fly.
Similarly, the spotted alfalfa aphid in controlled on most of
the U.S. alfalfa crop by host-plant resistance.   Resistance to
the pea aphid has also been bred into some alfalfa varieties and
is helping to control this pest.
To date, the most successful use of host-plant resistance has
been in the control of plant pathogens.   Breeding for disease
resistance is a widely used control strategy, and now most major
crop varieties have been developed to incorporate varying degrees
of resistance to one or more important diseases.   For some crops,
like small grains, up to 98 percent of the world total is planted
to resistant varieties.
In selecting and breeding plants for host-plant resistance to
pests, the nutrients or the level of chemical toxicants in the
new variety may be altered and the plant's resistance to pests
enhanced thereby.  For example, some standard maize varieties
with high levels of carotene (vitamin A) have been found to be
more resistant to maize leaf aphids than lines with lower levels
of carotene.  However, high levels of vitamin A can be harmful to
animals and humans, and such changes need not be beneficial to
humans and livestock using the maize.
In addition to variations in nutrient levels that often affect
levels of pest populations, many plants produce chemical toxins
that diminish or prevent pest attack.   For example, the potato
plant produces them in leaves, stems, and sometimes even in the
tuber.  At certain dosages these are toxic to some pests; unfortunately,
for potatoes that have turned green from being left in
sunlight, they can also poison humans.
Parasites and Predators for Biological Control
The deliberate use of predators and parasites, including microorganisms,
to control several insect pests has proved to be
highly successful.  The first effort to employ predators and
parasites for biological control occurred late in the 19th century
when the Australian Vedalia beetle was brought to California
to control the cottony-cushion scale on citrus [7).   Since then,
this technique has been used extensively on more than a million
hectares of crops including citrus and olive [2].   Effective
biological control in being achieved on other crops like apples,
alfalfa, and maize [7].  Possibly the most successful biological
control project to date is the importation from Argentina of a
wasp that (dropped from aircraft in Africa) parasitizes the
cassava mealybug.  This project has reduced cassava losses from 80
percent to 40 percent of the crop; the crop losses since 1973 are
estimated at $5.5 billion.
In addition to controlling insects, predators and parasites can
control plant pathogens.  Recent research at the USDA Beltsville
laboratory has demonstrated that one species of fungus parasitizes
a different one that causes 'leaf spot' in lettuce and
more than 200 other food crops.   Great potential exists for the
expanded use of biological control measures against plant pathogens.
Insects and microorganisms are also used to control weeds [7].
One of the most successful examples of this was the introduction
of two species of leaf-feeding beetles to control the Klamath
weed pest in California.  As a result, the weed has been controlled
effectively on more than 1.5 million hectares of cropland,
both in California and neighboring states.
Great care must be exercised in using plant-feeding insects and
plant pathogens for weed control, because they may pose a threat
to crop and natural plants in the total system.   No major problems
have resulted in modern times from the introduction of
biological controls for weeds.   Indeed, the existing levels of
risk are very low because of the ways that research is conducted
and its results made available to farmers.
Crop Rotation and Multiple Cropping
Rotation of crops is a most useful technique for controlling
pest insects, diseases, and weeds.   The adverse effect on pest
outbreaks of continuous culture of the same crop on the same land
has been discussed.  Therefore, it is not unexpected to find that
rotation of crops such as susceptible maize, in an appropriate
sequence with other crops, results in effective control of the
maize rootworm complex.  Multiple cropping and intercropping can
reduce pest populations and the damage they inflict.
Although many crop rotation programs help to control some pests,
inappropriate rotation of crops may cause other problems.  An
example of this is planting potatoes after a crop of pasture
grasses, which may result in serious wireworm problems.   This
emphasizes the need to take into account the total system when
managing crope and pests.
Timing of Planting
Some pests can be controlled, or their injury reduced, by planting
the crop when the pest is not present.  In this way, the most
susceptible stage of crop development does not coincide with the
peak of the pest population.   This strategy is used for controlling
the Hossian fly: large areas of wheat are planted well after
the Hessian fly has emerged and when a large percentage of the
population has died for lack of suitable host plants.   The technique
has also proved to be effective in reducing the damage
from root and crown rot in winter wheat and winter barley.
The prime risk is in exposing the newly planted crop to another
pest that may emerge at the new planting time.   Other risks of
altered planting times include exposing the crop to drought if
rainfall in less during the later cropping schedule, to frost if
planted too early, or to immaturity at harvest if planted too
Genetic Methods
The technique of releasing insects that have been sterilized by
gamma radiation or by chemical sterilants, to compete with other
insects for mates, has been highly successful with the screw-worm
fly.  Release of sterile screwworm males destroyed the reproductive
capacity of the screwworm fly population and eradicated the
pest from the United States and parts of Mexico.   In some parts
of California, it has been successful against the Mediterranean
fruit fly.  Although the goal in these cases was eradication, the
sterile-male technique is of potential value in IPM.   But the
technique is not successful against all kinds of insect pests,
and some pest populations may become "resistant" to it.  Other
genetic technologies such as introducing lethal genes and
male-producing genes also offer potential for insect-pest control.
There is a chance of releasing a new genotype that will present a
greater risk than those already present.   In addition, if some
pests are not completely sterile when released, they may reproduce
and contribute to the pest problem.   The risks are acceptably
small under today's conditions of agricultural research.
Water Management
The enhancement or curtailment of water supply to crops alters
the ecosystem and in this way sometimes helps to control insect
pests, plant diseases, and weeds.   For instance, irrigation of
alfalfa fields has been reported to encourage vigorous fungal
attacks on the spotted alfalfa aphid and pea aphid populations.
Limiting the application of irrigation water to only the root
area of a plant and avoiding wetting the leaves and fruit may
reduce certain disease outbreaks in apple and citrus crops.  The
flooding of rice fields has been managed to suppress certain weed
species [7].
Unsuitable water applications to crops can encourage plant pathogen
outbreaks such an scab on apple trees and mildew on cucurbit
Soil Management
Simple techniques such an tilling the soil often help to control
certain pests.  For example, U.S.  wireworm populations, which
have a two-year life cycle, can be reduced by plowing the fields
during the summer.  Mechanical injury, exposure to summer heat,
bird predation, and low humidities probably account for most of
the mortality in the wireworm populations.
Turning over the soil buries most plant pathogens present on the
surface, thereby reducing the chance for future crop infections
[3].  Worldwide, soil manipulation is the primary means of weed
control.  Young weeds are uprooted, buried, or disturbed, resulting
in a high mortality in weed populations, especially when
conditions are dry.
Tilling the soil destroys some pests effectively; however, at
the same time, tillage exposes the soil to wind and water erosion.
Soil erosion has become a major environmental problem in
the world and primarily is due to use of the plow for weed control.
The risks and benefits of this strategy must be evaluated.
Minimum tillage offers a different set of benefits and risks.
For years, agriculturalists have known that field sanitation is
an effective way to control insects, plant diseases, and weeds.
Plowing-under crop residues has, for a long time, proved to be an
effective technique for controlling various pests that otherwise
might over winter for the next growing season.   Many weeds drop
their seeds on the soil surface, and some species will not germinate
when plowed under.  But some weed seeds may survive for
many years in the soil.  Any technology that is employed to eliminate
sources of pest infestation will reduce the chances of pest
Destroying weeds and other vegetation close to crops to achieve a
clean culture, however, may not always be beneficial.   The grape
leafhopper and its parasite are normally maintained at low levels
on the blackberry growing in vineyard borders.   When the leafhopper
invades the grapes, the readily available parasites on
the blackberry invade the vineyard at the same time and provide
control of the leafhopper.  As a result, leaving wild blackberry
to grow adjacent to grape vineyards has helped to maintain a
parasite population that has provided the prime means of control
of the grape leafhopper.
Combination Plantings
Planting appropriate combinations of crops together may help to
reduce the pressure of major peats on each crop [5].   For example,
in central America, combinations of maize and beans grown together
have had fewer pest problems than either crop grown by
itself.  So far, this technology has not been used extensively in
other locations, but it deserves greater attention.
Although the combination planting of certain crops has advantages,
it may also result in more serious post outbreaks than if
each crop were grown as a monoculture.   For example, growing maize
in association with either cotton or tobacco is more likely to
increase some pest-insect populations than if the crops were
produced as monocultures.  The ecology of each crop must be
clearly understood before combinations are used.
To a limited extent, cardboard, plastic, and other types of
physical barriers have been used to control insects and weeds.
Thus, wrapping the stems of trees and shrubs with paper tape may
prevent insect borers from attacking them.
The most widespread and successful use of barriers has been in
weed control, where organic and black plastic mulches have proved
to be highly effective.  However, this technique is costly in
both labor and materials and is generally used with high-value
crops such as market-garden vegetables.
Although organic mulches are effective in controlling weeds,
they may encourage other pests such as slugs and mice.   Heavy
organic mulches may also reduce soil temperatures and thus reduce
germination and rate of growth of certain crops; plastic mulches
can increase water runoff from the crop fields and cause flooding
of other land.
Disease-free Propagation
Destruction of valuable crops by plant pathogens can be prevented
by planting only disease-free propagated material and thereby
eliminating the source of any plant pathogens.  In the United
States this practice is widespread, especially in fruit trees.
Now, nearly all fruit trees are certified disease-free nursery
Fortunately, no known risks are associated with this nonchemical
control technology when practiced as described above.
For the farmer, the main advantage of IPM is reducing the amount
of pesticide, that in used.  This reduces the cost of pest control
while protecting the environment and public health.
A weakness of IPM in the need for research to establish the
technologies, which are more complex and sophisticated than
routine spraying.  In addition, educating farmers in the use of
IPM technologies is more difficult than training then to spray
crops once a week or once in two weeks.
What are the immediate prospects for IPM in developing countries?
They are good in those situations where farmers can be educated
to monitor the pests in their crops and "treat only when necessary."
Local agricultural research and extension officials and
farmers often have a sense of the "economic-injury level" and can
thus develop an initial IPM program for "treating when necessary."
For the long term, devising pest-control strategies with the
necessary degree of sophistication will require the joint efforts
of such specialists as entomologists, plant pathologists, weed
specialists, agronomists, plant breeders, and horticulturalists.
1.  Davies, J.C., "Integrated Approaches to Pest Management:
    Principal Peats of Food." In Shemilt, L.W. (ed.), Chemistry
    and World Food Supplies: The New Frontiers, CHEMRAWN II, pp
    97-107. Oxford U.K.): Pergamon Press, 1983.
2.  Huffaker, C.B. ed., New Technology of Pest Control. New York:
    John Wiley, 1980 USA.
3.  Kennedy, Donald (Chmn.), Pest Control: An Assessment of
    Present and Alternative Technologies, vols. I-V. Washington,
    D.C.: National Academy of Sciences, 1975 USA.
4.  Oka, I. N. "The Potential for the Integration of Plant Resistance,
    Agronomic, Biological, Physical/Mechanical Techniques,
    and Pesticides for Pest Control in Farming Systems." In
    Shemilt, L.W. (ed.), Chemistry and World Supplies: The
    New Frontiers, CHEMRAWN II, pp 173-184. Oxford (U.K. : Pergamon
    Press, 1983.
5.  Pimentel, D. (ed.), CRC Handbook of Pest Management in Agriculture,
    Vols. I-III. CRC Handbook Series in Agriculture.
    Boca Raton, Florida: CRC Press, 1981 USA.
6.  Pimentel, D., "Agroecology and Economics." In Kogan, M.
    (ed.), Ecological Theory and Integrated Pest Management
    Practice, pp. 299-319. New York: John Wiley and Sons, 1986
7.  "Restoring the Quality of Our Environment," Report of the
    Environmental Pollution Panel, President's Science Advisory
    Committee. Washington, D.C.: The White House, 1965 USA.