By: Carolee Boyles, 4-H IPM Coordinator, Florida 4-H Department, and Dr. Philip G. Koehler, Extension Entomologist, Department of
Entomology and Nematology, IFAS, University of Florida, Gainesville 32611.
Revised by: Richard W. Gleason, Adjunct Assistant, Florida 4-H Department, IFAS, University of Florida.
Principal Investigators: Dr. James C. Northrop, Extension 4-H Youth Specialist, Florida 4-H Department and Dr. Philip G. Koehler, Extension
Entomologist, Department of Entomology and Nematology, IFAS, University of Florida.
This publication was developed through educational grants provided by the United States Department of Agriculture, Florida Power and
Light, and the Center for Environmental and Natural Resources, IFAS.
We gratefully acknowledge the assistance of Dr. Reece I. Sailer, Graduate Research Professor of Entomology, and various Extension
Specialists, IFAS, for reviewing this publication.
Karen McFadyen and Jane Wells provided the illustrations for this publication.
Using Natural Enemies to Manage Pests
C. A. Boyles and P. G. Koehler
To Help You the pest.
Most pesticides are made from the same
As you use this publication, watch for words materials as gas and oil. Gas and oil are also
written in italics. Look in the glossary in the used to apply pesticides. Through IPM, wiser
back for an explanation of these words. use of pesticides helps to save energy.
The purpose of this book is for you to learn
Statement of Purpose the basic ideas of IPM. You may learn how to
use natural enemies to manage pests safely,
In the 1960's and 1970's, people began to with less energy and lower costs.
worry about the harmful effects of pesticides For more information, check these
and other poisons. Pesticides are needed to publications, available from your County
manage many pests of man, his crops and Extension agent.
animals. To help protect soil, water and air (the Pest Management Where to Start? -
environment), man no longer uses some Circular 548
pesticides. All About Pests Circular 543
Integrated Pest Management (IPM) is an Cultural Practices to Manage Pests -
effective, but less harmful way of managing Circular 547
pests of all kinds. An IPM user looks at the Spraying Away Pests Circular 544
whole picture the pest, the host, and the Plants Protected from Pests Circular 546
environment. Then following IPM methods, the The ABC's of IPM Circular 549
user chooses one or several ways to manage
Managing Pests Naturally
Have you ever watched the animals around
you get their food?
A cat sneaks up on its prey. The prey might
be a rat or a mouse. Suddenly the cat leaps, and
the mouse is trapped under the cat's paw.
From man's point of view, the cat is doing
something beneficial or good. It is helping to
get rid of man's pests in a natural way. /
Rats and mice may eat man's food.
Sometimes they have diseases that may be
passed on to man by fleas and filth.
Rats and mice are pests of man. The cat is the
pest's natural enemy.
SUsing Natural Enemies The Idea of
Man can use natural enemies to help manage
many pests. This is called biological control.
The idea of biological control is simple. One
kind of organism is kept in balance by another
kind of organism.
Many kinds of pests can be managed
biologically. Insects can be managed by other
insects or by diseases. Weeds can be managed
by insects or by plant pathogens. Rodents can
be kept in check by larger animals, such as cats
Three Kinds of Natural Enemies
Natural enemies may manage pests in one of
1. A natural enemy may kill a pest and then
eat it. This kind of enemy is usually larger than
the pest it eats.
An example of this kind of natural enemy is
the cat that kills rats and mice.
The cat is called a predator. The rat is called
2. Some natural enemies feed on a pest from
the inside while the pest is still alive. Finally,
this causes the pest to die. This kind of natural
enemy is usually either an insect or a nematode
Some kinds of flies and wasps manage "-'A ^'
caterpillars in this way. The female fly lays her
eggs on the caterpillar. When the eggs hatch,
the fly larvae burrow into the caterpillar's body.
The larvae eat the caterpillar's insides. The .
caterpillar gets weaker and weaker and finally
dies. Then the fly larvae become pupae, and
finally hatch into adult flies. The cycle can then
This kind of natural enemy is called a
3. Some natural enemies infect organisms,
\ including pests. These natural enemies are very
S\ tiny organisms. You probably could not see
them without a microscope. But you can
certainly see their effects.
This kind of natural enemy is called a
pathogen. Pathogens give the pest a disease.
The pests most often managed by pathogens
I are insects and weeds.
Caterpillars on vegetables are often treated
this way. A bacteria called Bacillus thuringiensis
can be sprayed on the plants. When caterpillars
eat plants sprayed with this, they get sick and
There are many different kinds of natural man manage the harmful insects. Here are
enemies. Probably the largest group is the some illustrations of a few beneficial insects.
insect predators. These beneficial species help Learn to recognize these.
Beneficial Insects and Their Relatives
Ladybird Beetle and Garden Spider Braconid Wasp
Larva Parasitizing Aphid
Praying Mantis Earwig Ground Beetle
Tiger Beetle Syrphid Fly and Larva Tachinid Fly
Yellow Jacket Wasp Predaceous Flower Bug Honey Bee
Natural Enemies Work in Groups
In nature, organisms exist in groups. These
groups are called populations. A population is a
group of organisms of the same kind. That is,
they are all dogs, or cats, or horses, or house
flies. Members of the group can breed with
one another and have young.
Population density means the number of
organisms of one kind in a known area.
The population density may be low (such as
10 caterpillars in an acre of corn plants).
The population density may be high (such as
10 caterpillars in an ear of corn).
In nature, populations of organisms affect
one another. Predators eat their prey. Parasites
feed on hosts.
The way populations affect one another can
keep a pest organism from becoming a
problem. To explain this, let's talk about rats
and cats in a barn.
Suppose there is a small population of rats in
a barn. They feed on some scraps of hay and
grain lying on the barn floor.
Suppose there are also two cats that live in
the barn. They sometimes catch and eat a rat.
Because the cats do not have many rats to
eat, they do not have many kittens. The kittens
they do have may go away to live and hunt. So,
the population of cats stays about the same..
Because the rats do not have much to eat
either, they do not have many young rats.
Some of the rats that are born are soon eaten
by the cats. The population of rats also stays
about the same.
If conditions in the barn change, the
populations of both rats and cats may change.
For example, the farmer may place a lot of
grain in the barn. The rats suddenly have lots of
food. They start having many young. The size of
the rat population increases.
As the number of rats increases, the cats may /,
not be able to catch enough rats to keep the rat
population small. The number of rats keeps /
rising, and becomes a problem.
The cat population will also change. As the
cats have more to eat, they will have more
kittens. As the kittens grow up, they won't
leave. They will stay around and catch rats.
After a while, the cats may start catching Soon the cat population and the rat
more rats than are being born. The rat population will stop changing. The cats will
population will get smaller and smaller. There catch enough rats to keep the rat population
will not be enough rats for the cats to feed on. small. The rats will have enough young rats to
Hungry cats will again start to leave the cat feed the cat population.
population. They will look for food somewhere
These ideas can be applied to any biological It is important to understand that the effect a
control situation. The pest can be rats or natural enemy has on a pest is always changing.
caterpillars. The natural enemy can be cats or It depends on the population density of both
flies. The natural enemy works the same way in the pest and the natural enemy.
How Man Can Use
Man can use biological methods in four
1. The most important way to use biological
methods is to protect natural enemies.
Sometimes, in using pesticides, the helpful .-,
natural enemies may be killed. When this \
happens, the population of pests may increase. ,''
/ / I
-, / I
This is certainly not good. Therefore, we must
try to avoid killing natural enemies with
pesticides when possible.
Protecting natural enemies is called
2. Sometimes, there aren't enough natural
enemies to manage the pests. Then more
natural enemies can be released.
For example, suppose there are very many
rats but only one or two cats. The cats will not
be able to hold down the rats. The farmer can
release many more cats to help get rid of the
Managing pests by flooding them with
natural enemies is called inundation.
S3. Some of our pests have come from other
L,,, S\parts of the world. They have accidentally been
brought into this part of the country. Here they
C' \have become pests because they have no
,,-" Scientists can look for natural enemies where
the pest came from. Then they can bring the
natural enemies to the pest.
Bringing in a new natural enemy from
another area is called importation. Scientists
must be very careful when they import a A -
natural enemy. They must be sure that the
enemy will eat ONLY the pest. They must also
know if any organisms will harm the imported
enemy. Also, they should import only the
natural enemy, and no other organisms.
4. Small numbers of a natural enemy can be
released into an area where there are none.
This will start a population of the enemy.
For example, a farmer may release a few cats
in a barn where there are lots of rats. For a
while, there will not be enough cats to manage
the rats. But eventually the cat population gets
larger. Then there will be enough cats to
manage the rats.
Helping a population of natural enemies to
get started in called inoculation.
How Biological Methods
Biological methods are different from other
pest management tools. These differences may
be good or bad. It depends on the situation.
1. Natural enemies do not work as fast as
pesticides do. It takes time for a natural enemy
to control a pest.
2. If a natural enemy does manage the pest,
the natural enemy may keep on working for a
3. Natural enemies do not control all of the
pests in an area. There is always a small
population of the pest. Therefore, the natural
enemy always has food.
4. Most kinds of biological methods are Also, most biological methods do not require
harder to use than pesticides. They are also a lot of energy use to work well. So, biological
harder to misuse than pesticides because they methods of pest management help conserve
are not poisons. energy.
poisonous non-po sonous
How Biological Methods Are Used in Cultural practices
IPM Host resistance methods
In Pest Management Where to Start, you
Biological methods are an important tool in also learned about the six-step IPM process:
an Integrated Pest Management program. Step 1. Identification
You learned about all of the IPM tools in Pest Step 2. Prevention
Management Where to Start Circular 548. Step 3. Monitoring
Biological methods Step 4. Prediction
Mechanical methods Step 5. Decision
Physical methods Step 6. Evaluation
Regulatory methods Biological methods are used at several steps
Chemical methods in an IPM program.
At Step 1, Identification, natural enemies
must be identified.
At Step 2, Prevention, natural enemies must
be protected. This helps keep pest populations
from growing large enough to become a
problem. The best way to do this is to use as
few pesticides as possible.
...... .. .. ....... '
At Step 3, Monitoring, populations of pests '*......
and natural enemies must be counted. This
helps make predictions about damage by pests.
Prediction is Step 4.
If the natural enemies do not manage the
pests, a decision must be made at Step 5. There
are three choices that can be made:
1. Help natural enemies by conservation, S O
importation, inundation, or inoculation (using
2. Apply a pesticide. A pesticide can be used
to kill the pest. Unfortunately, it may kill some
natural enemies as well. Many IPM programs
rely on natural enemies to manage pests. In
these programs, pesticides should be used only
as a last resort.
3. Do nothing. The cost of either helping the Using IPM Tools Together
natural enemy or applying a pesticide may be When beginning an IPM program, a
too high. If so, a decision may be made to do homeowner or producer needs to consider
nothing. this. How will the different tools of pest
management affect each other? Using a natural
enemy will not affect how the other tools of
IPM work. The other tools of IPM, though, will
affect how well a natural enemy manages a
1. Beneficial Helpful; something that is becomes a pupa, and then an adult. Some
good, or that helps something else. kinds of larvae are caterpillars, or maggots,
2. Density The population in a known or grubs.
area. 7. Misused Used wrongly or improperly.
3. Environment Surroundings, including 8. Natural enemy An organism that kills
anything that affects man, other animals or and eats, or lives on another organism.
plants. 9. Nematode A tiny worm-like organism
4. Host Any plant or animal that shelters that lives in the soil and damages the roots
or gives a home to a parasite or other of plants. Nematodes may live in the soil,
natural enemy, in water, in animals, or in plants.
5. Infect To contaminate as to cause 10. Organisms Living things; includes all
disease. animals and plants.
6. Larva One stage in the life of some 11. Parasites An animal or plant that lives
insects. A larva hatches from an egg. When on or in another organism, from which it
it has grown as large as it is going to, it gets food and shelter. In IPM, a natural
enemy that kills pests. Parasites are usually
smaller than the pests. Example: fly (0
maggots eating large caterpillars.
12. Pathogen Very tiny organism that
causes a disease. The three types of
pathogens are fungi, bacteria, and viruses.
13. Pest An organism that hurts something
or is bad for something that belongs to /
man. A pest may be an insect, a plant, an
animal, a disease, or any other kind of
14. Pesticides Poisons that are used to kill 6 /
organisms that man regards as pests.
Insecticides kill insects. Herbicides kill
plants. Fungicides kill fungi.
15. Population A group of organisms, all of
the same species, that lives in an area.
They are capable of reproducing.
16. Predators Natural enemies that kill and
eat pests. Predators are usually larger than
pests. Example: cat = predator, mouse =
17. Prey An organism that a predator
catches and eats.
18. Pupa One stage in the life of some
insects. Some pupae are also called
cocoons. A pupa is the "resting" stage in
the insect's life. An adult insect will hatch
from it. Pupae Plural of pupa.
19. Species One kind of plant or animal; a
group of plants or animals that are alike.
Man is one species. Dogs are one species.
One species may have different varieties.
For instance, German Shepherd and
Doberman are varieties of dogs.
This publication was promulgated at a cost of $812.00, or 30 cents per copy, to inform Florida residents about
IPM (Integrated Pest Management). 5-2700-83
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL
SCIENCES, K. R. Tefertller, director, in cooperation with the United States Department of Agriculture, publishes this infor-
matlon to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and is authorized to provide research, educa-
tional Information and other services only to individuals and institutions that function without regard to race, color, sex or
national origin. Single copies of Extension publications (excluding 4-H and Youth publications) are available free to Florida
residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers Is available from
C. M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this
publication, editors should contact this address to determine availability.