Biological Control and Natural Enemies

1. Biological Control and
Natural Enemies
Integrated Pest Management for Home Gardeners and Landscape Professionals
Biological control is the beneficial are sometimes drastically reduced ticides, but applying these products
action of predators, parasites, patho- by naturally occurring pathogens, is not considered to be biological
gens, and competitors in controlling usually under conditions such as pro- control.
pests and their damage. Biocontrol longed high humidity or dense pest
provided by these living organ- populations. In addition to naturally Parasites
isms (collectively called “natural occurring disease outbreaks, some A parasite is an organism that lives
enemies”) is especially important for beneficial pathogens are commer- and feeds in or on a larger host.
reducing the numbers of pest insects cially available as biological or micro- Insect parasites (more precisely
and mites (Table 1). Natural enemies bial pesticides. These include Bacillus called parasitoids) are smaller than
also control certain rangeland and thuringiensis or Bt, entomopathogenic their host and develop inside, or
wildland weeds, such as Klamath nematodes, and granulosis viruses. attach to the outside, of the host’s
weed (St. Johnswort). Plant patho- Additionally, some microorganism body. Often only the immature stage
gens, nematodes, and vertebrates also by-products such as avermectins and of the parasite feeds on the host, and
have many natural enemies, but this spinosyns are used in certain insec- it kills only one host individual dur-
biological control is often harder to
recognize, less-well understood, or
more difficult to manage. Conserva-
tion, augmentation, and classical
biological control (also called impor-
tation) are tactics for harnessing the
effects of natural enemies.
TYPES OF NATURAL
ENEMIES
Predators, parasites, and pathogens
are the primary groups used in A. Egg B. Larva
biological control of insects. Most
parasites and pathogens, and many
predators, are highly specialized and
attack only one or several closely
related pest species. Learn how to
recognize natural enemies by con-
sulting resources such as the Natural
Enemies Handbook and the Natural
Enemies Gallery online at http://
www.ipm.ucdavis.edu.
D. Adult C. Pupa
Pathogens
Pathogens are microorganisms
Figure 1. In many cases, only the immature stage of a parasite feeds on the host, as
including certain bacteria, fungi, illustrated here with a species that attacks aphids. A. An adult parasite lays an egg
nematodes, protozoa, and viruses inside a live aphid. B. The egg hatches into a parasite larva that grows as it feeds
that can infect and kill the host. on the aphid’s insides. C. After killing the aphid, the parasite pupates. D. The wasp
Populations of some aphids, caterpil- chews a hole and emerges from the dead aphid, then flies off to find and parasitize
lars, mites, and other invertebrates other aphids.
PEST NOTES
University of California
Publication 74140
Agriculture and Natural Resources October 2007

2. October 2007 Biological Control and Natural Enemies
Table 1. Some pests and their common natural enemies.
Natural Enemies
Predatory mites
Parasitic wasps
Pests
Parasitic flies
Lady beetles
Lacewings
Other groups and examples
entomopathogenic fungi
aphids
•
•
•
syrphid fly larvae
carpenterworm, • entomopathogenic nematodes
clearwing moth larvae
Bacillus thuringiensis
birds
caterpillars (e.g., California pathogenic fungi and viruses
•
•
•
oakworm) predaceous wasps
Trichogramma spp.(egg parasitic wasps)
spiders
Cryptochaetum iceryae (parasitic fly)
cottony cushion scale
•
•
vedalia beetle
Erynniopsis antennata (parasitic fly)
elm leaf beetle
•
•
Oomyzus (=Tetrastichus) spp. (parasitic wasps)
Avetianella longoi (egg parasitic wasp)
eucalyptus longhorned borers
•
Syngaster lepidus (larval parasitic wasp)
eucalyptus redgum lerp psyllid Psyllaephagus bliteus (parasitic wasp)
•
•
Entedononecremnus krauteri, Encarsiella noyesii, and
giant whitefly
•
•
•
•
Idioporus affinis (parasitic wasp)
glassy-winged sharpshooter Gonatocerus spp. (egg parasitic wasps)
•
pirate bugs
lace bugs
spiders
•
•
•
mealybugs mealybug destroyer lady beetle
•
•
•
•
mosquitoes Bacillus thuringiensis ssp. israelensis
psyllids pirate bugs
•
•
•
scales Aphytis spp. (armored scale parasites)
•
•
•
•
Rumina decollata (predatory snail)
slugs, snails predaceous ground beetles
•
vertebrates
sixspotted thrips
spider mites
•
•
•
Stethorus picipes (spider mite destroyer lady beetle)
thrips predatory thrips
•
•
Steinernema carpocapsae and
weevils, root or soil-dwelling Heterorhabditis bacteriophora (entomopathogenic
nematodes)
Encarsia formosa (greenhouse whitefly parasite)
whiteflies
pirate bugs
•
•
•
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3. October 2007 Biological Control and Natural Enemies
ing its development (Figure 1). How- spp., Neoseiulus spp., and the western groups.
ever, adult females of certain para- predatory mite (Galendromus occiden-
sites (such as many wasps that attack talis). CONSERVATION:
scales and whiteflies) feed on their PROTECT YOUR
hosts, providing an easily overlooked Recognizing Natural Enemies. NATURAL ENEMIES
but important source of biological Proper identification of pests, and Preserve naturally occurring benefi-
control in addition to the host mortal- distinguishing pests from their cial organisms whenever possible.
ity caused by parasitism. natural enemies, are essential to Most pests are attacked by several
effectively using biological control. different types and species of natural
Most parasitic insects are either flies For example, some people may mis- enemies, and their conservation is the
(Diptera) or wasps (Hymenoptera). take aphid-eating syrphid fly larvae primary way to successfully use bio-
Parasitic Hymenoptera occur in over for caterpillars. The adult syrphid, logical control in gardens and land-
three dozen families. For example, commonly also called a flower fly or scapes (Figure 2). Ant control, habitat
Aphidiinae (a subfamily of Braco- hover fly, is sometimes mistaken for manipulation, and selective pesticide
nidae) attack aphids. Trichogram- a honey bee. Consult publications use are key conservation strategies.
matidae parasitize insect eggs. Aph- such as the UC Statewide Integrated
elinidae, Encyrtidae, Eulophidae, and Pest Management Program Pest Notes Pesticide Management
Ichneumonidae are other groups of series listed in Suggested Reading Broad-spectrum pesticides often kill
tiny size to medium-sized wasps that to learn more about the specific a higher proportion of predators and
parasitize pests but do not sting peo- pests and their natural enemies in parasites than of the pest species
ple. The most common parasitic flies your gardens and landscapes. Take they are applied to control. In addi-
are Tachinidae. Adult tachinids often unfamiliar organisms you find to tion to immediately killing natural
resemble house flies. Their larvae are your Cooperative Extension office or enemies that are present (contact tox-
county agriculture commissioner for icity), many pesticides are persistent
maggots that feed inside the host.
materials that leave residues that kill
an expert identification. Carefully
natural enemies that migrate in after
Predators observe the creatures on your plants
spraying (residual toxicity). Residues
Insects are important food for many to help discern their activity. For
often are toxic to natural enemies
amphibians, birds, mammals, and example, to distinguish plant-feed-
long after pests are no longer affected.
reptiles. Many beetles, true bugs ing mites from predaceous mites,
Even if beneficials survive an applica-
(Hemiptera or Heteroptera), flies, observe them on your plants with a
tion, low levels of pesticide residues
and lacewings are predators of vari- good hand lens. Predaceous species
can interfere with natural enemies’
ous pest mites and insects (Table 2). appear more active than plant-feed-
reproduction and their ability to
Most spiders feed entirely on insects. ing species. In comparison with pest
locate and kill pests.
Predatory mites that prey primarily mites, predaceous mites are often
on spider mites include Amblyseius larger and do not occur in large Biological control’s importance often
becomes apparent when broad-spec-
Table 2. Some important predaceous insects.
trum, persistent pesticides cause
Common name Examples secondary pest outbreaks or pest
resurgence. A secondary outbreak
aphid flies Chamaemyia spp., Leucopis spp. of a different species occurs when
assassin bugs Zelus renardii pesticides applied against a target
pest kill natural enemies of other spe-
brown lacewings Hemerobius spp. cies, causing the formerly innocuous
green lacewings Chrysopa spp., Chrysoperla spp. species to become pests (Figure 3).
An example is the dramatic increase
ground beetles Calosoma spp., Calathus spp. in spider mite populations that
sometimes results after applying a
lady beetles convergent lady beetle, mealybug destroyer,
multicolored Asian lady beetle carbamate (e.g., carbaryl or Sevin) or
organophosphate (malathion) to con-
minute pirate bugs Orius spp., Anthocoris spp. trol caterpillars or other pests.
predaceous midges (aphid midges) Aphidoletes aphidimyza
Eliminate or reduce the use of broad-
predaceous thrips black hunter thrips, sixspotted thrips spectrum, persistent pesticides
whenever possible. Carbamates,
soldier beetles Cantharis spp.
organophosphates, and pyrethroids
syrphid flies (flower flies, hover flies) Metasyrphus spp., Scaeva spp. are especially toxic to natural
enemies (Table 3). When pesticides
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4. October 2007 Biological Control and Natural Enemies
are used, apply them in a selective
manner. Treat only heavily infested
spots instead of entire plants. Choose
insecticides that are more specific
in the types of invertebrates they
kill, such as Bacillus thuringiensis (Bt)
that kills only caterpillars that eat
treated foliage. Rely on insecticides
with little or no persistence, includ-
ing insecticidal soap, horticultural or
narrow-range oil, and pyrethrins.
A less-persistent pesticide can result
in longer control of the pest in situ-
ations where biological control is
important because the softer pes-
ticide will not keep killing natural
enemies. One soft pesticide spray
plus natural enemies can be effective
for longer than the application of one
hard spray.
Ant Control and Honeydew
Figure 2. Most pests are attacked by a complex of natural enemies. Shown here is a Producers
lace bug surrounded by its common predators. Conserving these beneficial species Ants are beneficial as consumers
is the primary way to successfully use biological control in gardens and landscapes. of weed seeds, predators of many
Each pest life stage can be killed by various other species of parasites, pathogens, insect pests, soil builders, and nutri-
and predators not illustrated here. ent cyclers. Ants may attack people
and pets or are direct pests of crops,
feeding on nuts or fruit (See Pest
Table 3. Relative toxicity to natural enemies of certain insecticide groups. Notes: Red Imported Fire Ants). The
Argentine ant and certain other spe-
cies are pests primarily because
they feed on honeydew produced by
Insecticide Toxicity
Homopteran insects such as aphids,
mealybugs, soft scales, and whiteflies.
Bacillus thuringiensis (Bt) No contact—No residual Ants protect honeydew producers
from predators and parasites that
botanicals (e.g., azadirachtin, Moderate to high contact—No residual to
might otherwise control them. Ants
pyrethrins), oils, soaps, spinosad short residual sometimes move these honeydew-
producing insects from plant to plant.
chloronicotinyls (imidacloprid, Bayer Low to high1 Where natural enemies are present,
Advanced Tree & Shrub or Merit) if ants are controlled, populations of
many pests will gradually (over sev-
carbamates (carbaryl or Sevin), High contact—Long residual
organophosphates (malathion), eral generations of pests) be reduced
pyrethroids (permethrin) as natural enemies become more
abundant. Control methods include
cultivating soil around ant nests,
Direct contact toxicity is killing within several hours from spraying the beneficial or its
habitat.
encircling trunks with ant barriers,
Residual toxicity is killing or sublethal effects (such as reduced reproduction or and applying insecticide baits near
impaired ability to locate and kill pests) due to residues that persist. plants. See Pest Notes: Ants for more
information.
1Toxicity and persistence are highly variable, depending partly on the application
method (foliar spray vs. soil drench) and the life stage and species of the natural Habitat Manipulation
enemy.
Manage gardens and landscapes
by using cultural and mechanical
methods that enhance natural enemy
effectiveness. Grow diverse plant
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5. October 2007 Biological Control and Natural Enemies
species and tolerate low populations ever, lady beetles purchased through native habitat, study and collect the
of plant-feeding insects and mites so retail outlets are unlikely to be suf- natural enemies that kill the pest
that some food is always available to ficient in numbers and quality to pro- there, and then ship promising natu-
retain predators and parasites. Plant vide control. ral enemies back for testing and pos-
a variety of sequentially flowering sible release. Many insects and some
species to provide natural enemies Successful augmentation generally weeds that were widespread pests
with nectar, pollen, and shelter requires advanced planning, bio- in California are now partially or
throughout the growing season. The logical expertise, careful monitoring, completely controlled by introduced
adult stage of many insects with pre- optimal release timing, patience, and natural enemies, except where these
daceous larvae (such as green lace- situations where certain levels of natural enemies are disrupted, such
wings and syrphid flies) and many pests and damage can be tolerated. as by pesticide applications or honey-
adult parasites feed only on pollen Desperate problems where pests or dew-seeking ants.
and nectar. Even if pests are abun- damage are already abundant are not
dant for the predaceous and parasitic good opportunities for augmentation. Natural enemy importation by law
stages, many beneficials will do must be done only by qualified sci-
poorly unless flowering and nectar- CLASSICAL BIOLOGICAL entists with government permits.
producing plants are available to CONTROL OR Natural enemies are held and studied
adult natural enemies. Reduce dust, IMPORTATION in an approved quarantine facility to
for example, by planting ground Classical biological control, also prevent their escape until research
covers and windbreaks. Dust can called importation, is primarily used confirms that the natural enemy will
interfere with natural enemies and against exotic pests that have inad- have minimal negative impact in the
may cause outbreaks of pests such as vertently been introduced from else- new country of release. Because clas-
spider mites. Avoid excess fertiliza- where. Many organisms that are not sical biological control can provide
tion and irrigation, which can cause pests in their native habitat become long-term benefits over a large area
phloem-feeding pests such as aphids unusually abundant after colonizing and is funded through taxes, pub-
to reproduce more rapidly than natu- new locations without their natural lic support is critical for continued
ral enemies can provide control. controls. Researchers go to the pest’s success. Consult Natural Enemies
AUGMENTATION
When resident natural enemies are
insufficient, their populations can
Pest A: aphids
sometimes be increased (augmented)
through the purchase and release Pest B: spider mites
of commercially available beneficial Natural enemies:
species. However, there has been
green lacewing larvae
relatively little research on releas-
ing natural enemies in gardens and predatory mites
landscapes. Releases are unlikely to
provide satisfactory pest control in
most situations. Some marketed nat-
ural enemies are not effective. Pray-
ing mantids, often sold as egg cases,
make fascinating pets. But mantids
are cannibalistic and feed indiscrimi-
nately on pest and beneficial species.
Releasing mantids does not control
pests.
A pesticide applied to control pest A Released from the control exerted by
also kills natural enemies that are natural enemies, pest B builds up to
Only a few natural enemies can be controlling pest B. economically damaging levels.
effectively augmented in gardens and
landscapes. These include entomoph-
agous nematodes, predatory mites, Figure 3. Killing natural enemies often results in secondary outbreaks of insects
and mites. For example, spider mites are often present on plants at low densities but
and perhaps a few other species. For
become excessively abundant and cause damage when pesticides applied against
example, convergent lady beetles other species kill the natural enemies of the spider mites. Here a pesticide applied to
(Hippodamia convergens) purchased in kill aphids (Pest A) not only killed aphids but also killed predaceous green lacewing
bulk through mail order and released larvae and predatory mites, leading to a secondary outbreak of spider mites (Pest B).
in very large numbers at intervals Insecticides applied during hot weather appear to have the greatest effect on mites,
can temporarily control aphids; how- sometimes causing dramatic mite outbreaks within a few days after spraying.
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6. October 2007 Biological Control and Natural Enemies
Handbook and Pests of Landscape Trees control. Natural enemies that do not WORLD WIDE WEB SITES
and Shrubs to learn about situations arrive or become abundant until after Biological Control: A Guide to Natu-
where imported natural enemies are pests are very abundant may not pre- ral Enemies in North America. Cor-
important and conserve them when- vent serious damage to plants. Con- nell University. www.nysaes.cornell
ever possible. versely, a parasite or predator with .edu/ent/biocontrol
multiple annual generations, that can
Is Biological Control “Safe”? attack a broad range of life stages of Biological Control Information Cen-
One of the great benefits of biologi- the pest and can feed and reproduce ter North Carolina State Univ. http://
cal control is its relative safety for when pest populations are low or cipm.ncsu.edu/ent/biocontrol
human health and the environ- moderate, will likely be a more effec-
ment. Most negative impacts from tive natural enemy. Biological Control News, Midwest
exotic species have been caused by University of Wisconsin-Madison,
undesirable organisms contaminat- Dept. of Entomology. www.entomol-
ing imported goods, by travelers SUGGESTED READING ogy.wisc.edu/mbcn/mbcn.html
carrying in pest-infested fruit, by 1Natural Enemies Handbook: The Illus-
introduced ornamentals that escape trated Guide to Biological Pest Control. Center for Biological Control, www.
cultivation and become weeds, and 1998. M. L. Flint and S. H. Dreistadt. cnr.berkeley.edu/biocon
by poorly conceived importations Univ. Calif. Div. Agric. Nat. Res. Publ.
of predatory vertebrates like mon- 3386. Oakland. UC Statewide IPM Program Natural
gooses. These ill-advised or illegal Enemies Gallery, an online photo-
importations are not part of biologi- 1Pest Notes: Ants. Feb. 2007. M. K. Rust graphic reference, www.ipm
cal control. To avoid these problems, and J. H. Klotz. Oakland. Univ. Calif. .ucdavis.edu/PMG/NE/index.html v
biological control researchers follow Agric. Nat. Res. Publ. 7411. Also avail-
regulations and work with relatively able online, http://www.ipm.ucdavis.
host-specific insects. edu/PMG/menu.invertebrate.html 1
University of California Agriculture and Natural
Resource publications may be ordered online or
Help preserve our environment and 1 Pest Notes: Red Imported Fire Ant. via telephone.
avoid introducing exotic new pests. Sept. 2007. L. Greenberg, J. H. Klotz, • Toll free order line: (800) 994-8849
and J. N. Kabashima. Oakland. Univ. • Voice: (510) 642-2431
• Fax: (510) 643-5470
Do not bring uncertified fruit, plants, Calif. Agric. Nat. Res. Publ. 7487. Also • http://anrcatalog.ucdavis.edu
or soil into California. Take unfamil- available online, http://www.ipm
iar pests to your county agricultural .ucdavis.edu/PMG/menu.invertebrate
commissioner or Cooperative Exten- .html
sion office for identification.
1Pest Notes: Spiders. In press. R. S. Vet-
WHAT MAKES ter. Oakland. Univ. Calif. Agric. Nat.
AN EFFECTIVE Res. Publ. 7442. Also available online,
NATURAL ENEMY? http://www.ipm.ucdavis.edu/PMG/
Although many animals prey on menu.invertebrate.html
pest insects or mites, not all can be
relied upon to reduce a pest popula- 1Pest Notes: Spider Mites. Dec. 2000. B.
tion enough to protect plants. The Ohlendorf and M. L. Flint, eds. Oak-
most effective natural enemies are land. Univ. Calif. Agric. Nat. Res. Publ.
often relatively host specific, feeding 7405. Also available online, http://
on a single pest species or a group www.ipm.ucdavis.edu/PMG/menu.
of similar pests such as aphids or invertebrate.html
scales. Good examples include preda-
tory mites, most parasitic wasps, and 1Pests of Landscape Trees and Shrubs.
syrphid flies. Very general predators 2004. S. H. Dreistadt, M. L. Flint, and
such as praying mantids are often J. K. Clark. Univ. Calif. Agric. Nat.
likely to kill as many beneficials as Res. Publ. 3359. Oakland.
pests and thus rarely provide effec-
tive control.
Synchronization of the life cycle and
environmental requirements of the
pest and natural enemy also deter-
mine the effectiveness of biological
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7. October 2007 Biological Control and Natural Enemies
For more information contact the University
of California Cooperative Extension in your
county. See your telephone directory for
addresses and phone numbers.
AUTHOR: S. H. Dreistadt, UC Statewide IPM
Program, Davis
TECHNICAL EDITOR: M. L. Flint
COORDINATION & PRODUCTION: P. N. Galin
ILLUSTRATIONS: Fig. 1: D. Kidd.
Fig. 2: assassin bug: Zimmerman, E. C.
1948. Insects of Hawaii. Volume 3: Heterop-
tera. Honolulu: University of Hawaii Press;
lacewing larva and pirate bug: by Celeste
Green in Smith, R. F., and K. S. Hagen.
1956. Enemies of spotted alfalfa aphid. Calif.
Agric. 10(4):8–10; lady beetle: Simanton, F.
L. 1916. Hyperaspis binotata, a predatory
enemy of the terrapin scale. J. Agric. Res.
6:197–204; spider: Costello, M. J., M. A.
Mayse, K. M. Daane, W. A. O’Keefe, and C.
B. Sisk. 1995. Spiders in San Joaquin Valley
Grape Vineyards. Oakland. Univ. Calif. Div.
Agric. Nat. Res. Leaflet 21530; predatory
mite: Denmark, H. A., and E. Schicha. 1983.
Revision of the genus Phytoseiulus Evans
(Acarina: Phytoseiidae). Internat. J. Acarol.
9:27–35;. Fig. 3: V. Winemiller.
WARNING ON THE USE OF CHEMICALS
Produced by UC Statewide IPM Program, Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendations
University of California, Davis, CA 95616 given on the container label. Store all chemicals in the original labeled containers in a locked cabinet or shed,
away from food or feeds, and out of the reach of children, unauthorized persons, pets, and livestock.
This Pest Note is available on the Pesticides applied in your home and landscape can move and contaminate creeks, rivers, and oceans.
Confine chemicals to the property being treated. Avoid drift onto neighboring properties, especially gardens
World Wide Web (www.ipm.ucdavis.edu)
containing fruits or vegetables ready to be picked.
Do not place containers containing pesticide in the trash or pour pesticides down sink or toilet. Either use
the pesticide according to the label or take unwanted pesticides to a Household Hazardous Waste Collection
site. Contact your county agricultural commissioner for additional information on safe container disposal and
for the location of the Household Hazardous Waste Collection site nearest you. Dispose of empty containers
by following label directions. Never reuse or burn the containers or dispose of them in such a manner that
they may contaminate water supplies or natural waterways.
This publication has been anonymously peer
reviewed for technical accuracy by University of
The University of California prohibits discrimination or harassment of any person on the basis of race,
California scientists and other qualified profession-
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Associate Editor for Urban Pest Management. or genetic characteristics), ancestry, marital status, age, sexual orientation, citizenship, or status as a
To simplify information, trade names of products covered veteran (covered veterans are special disabled veterans, recently separated veterans, Vietnam
have been used. No endorsement of named products era veterans, or any other veterans who served on active duty during a war or in a campaign or expedi-
is intended, nor is criticism implied of similar products tion for which a campaign badge has been authorized) in any of its programs or activities. University
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This material is partially based upon work supported regarding the University’s nondiscrimination policies may be directed to the Affirmative Action/Staff Per-
by the Extension Service, U.S. Department of sonnel Services Equal Opportunity Director, University of California, Agriculture and Natural Resources,
Agriculture, under special project Section 3(d), 1111 Franklin Street, 6th Floor, Oakland, CA 94607, (510) 987-0096
Integrated Pest Management.
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