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Biological Control and Natural Enemies Integrated Pest Management for Home Gardeners and Landscape ProfessionalsBiological control is the beneficial are sometimes drastically reduced ticides, but applying these productsaction of predators, parasites, patho- by naturally occurring pathogens, is not considered to be biologicalgens, and competitors in controlling usually under conditions such as pro- control.pests and their damage. Biocontrol longed high humidity or dense pestprovided by these living organ- populations. In addition to naturally Parasitesisms (collectively called “natural occurring disease outbreaks, some A parasite is an organism that livesenemies”) 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 preciselyand mites (Table 1). Natural enemies bial pesticides. These include Bacillus called parasitoids) are smaller thanalso control certain rangeland and thuringiensis or Bt, entomopathogenic their host and develop inside, orwildland weeds, such as Klamath nematodes, and granulosis viruses. attach to the outside, of the host’sweed (St. Johnswort). Plant patho- Additionally, some microorganism body. Often only the immature stagegens, nematodes, and vertebrates also by-products such as avermectins and of the parasite feeds on the host, andhave many natural enemies, but this spinosyns are used in certain insec- it kills only one host individual dur-biological control is often harder torecognize, less-well understood, ormore difficult to manage. Conserva-tion, augmentation, and classicalbiological control (also called impor-tation) are tactics for harnessing theeffects of natural enemies.TYPES OF NATURALENEMIESPredators, parasites, and pathogensare the primary groups used in A. Egg B. Larvabiological control of insects. Mostparasites and pathogens, and manypredators, are highly specialized andattack only one or several closelyrelated pest species. Learn how torecognize natural enemies by con-sulting resources such as the NaturalEnemies Handbook and the NaturalEnemies Gallery online at http://www.ipm.ucdavis.edu. D. Adult C. PupaPathogensPathogens are microorganisms Figure 1. In many cases, only the immature stage of a parasite feeds on the host, asincluding certain bacteria, fungi, illustrated here with a species that attacks aphids. A. An adult parasite lays an eggnematodes, protozoa, and viruses inside a live aphid. B. The egg hatches into a parasite larva that grows as it feedsthat can infect and kill the host. on the aphid’s insides. C. After killing the aphid, the parasite pupates. D. The waspPopulations of some aphids, caterpil- chews a hole and emerges from the dead aphid, then flies off to find and parasitizelars, mites, and other invertebrates other aphids.PEST NOTES University of California Publication 74140 Agriculture and Natural Resources October 2007
October 2007 Biological Control and Natural Enemiesing 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 YOURhosts, providing an easily overlooked Recognizing Natural Enemies. NATURAL ENEMIESbut 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 naturalMost 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, habitatAphidiinae (a subfamily of Braco- hover fly, is sometimes mistaken for manipulation, and selective pesticidenidae) attack aphids. Trichogram- a honey bee. Consult publications use are key conservation strategies.matidae parasitize insect eggs. Aph- such as the UC Statewide Integratedelinidae, Encyrtidae, Eulophidae, and Pest Management Program Pest Notes Pesticide ManagementIchneumonidae are other groups of series listed in Suggested Reading Broad-spectrum pesticides often killtiny size to medium-sized wasps that to learn more about the specific a higher proportion of predators andparasitize pests but do not sting peo- pests and their natural enemies in parasites than of the pest speciesple. 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 naturalresemble house flies. Their larvae are your Cooperative Extension office or enemies that are present (contact tox- county agriculture commissioner for icity), many pesticides are persistentmaggots that feed inside the host. materials that leave residues that kill an expert identification. Carefully natural enemies that migrate in afterPredators observe the creatures on your plants spraying (residual toxicity). ResiduesInsects are important food for many to help discern their activity. For often are toxic to natural enemiesamphibians, 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 residuesand 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 toMost spiders feed entirely on insects. ing species. In comparison with pest locate and kill pests.Predatory mites that prey primarily mites, predaceous mites are oftenon 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 ◆ 3 of 7 ◆
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 HoneydewFigure 2. Most pests are attacked by a complex of natural enemies. Shown here is a Producerslace bug surrounded by its common predators. Conserving these beneficial species Ants are beneficial as consumersis the primary way to successfully use biological control in gardens and landscapes. of weed seeds, predators of manyEach 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 ◆ 4 of 7 ◆
October 2007 Biological Control and Natural Enemiesspecies and tolerate low populations ever, lady beetles purchased through native habitat, study and collect theof plant-feeding insects and mites so retail outlets are unlikely to be suf- natural enemies that kill the pestthat 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 somespecies to provide natural enemies Successful augmentation generally weeds that were widespread pestswith nectar, pollen, and shelter requires advanced planning, bio- in California are now partially orthroughout the growing season. The logical expertise, careful monitoring, completely controlled by introducedadult stage of many insects with pre- optimal release timing, patience, and natural enemies, except where thesedaceous larvae (such as green lace- situations where certain levels of natural enemies are disrupted, suchwings 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 notdant for the predaceous and parasitic good opportunities for augmentation. Natural enemy importation by lawstages, 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 studiedadult natural enemies. Reduce dust, IMPORTATION in an approved quarantine facility tofor example, by planting ground Classical biological control, also prevent their escape until researchcovers and windbreaks. Dust can called importation, is primarily used confirms that the natural enemy willinterfere with natural enemies and against exotic pests that have inad- have minimal negative impact in themay 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 providetion and irrigation, which can cause pests in their native habitat become long-term benefits over a large areaphloem-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 continuedral enemies can provide control. controls. Researchers go to the pest’s success. Consult Natural EnemiesAUGMENTATIONWhen resident natural enemies areinsufficient, their populations can Pest A: aphidssometimes be increased (augmented)through the purchase and release Pest B: spider mitesof commercially available beneficial Natural enemies:species. However, there has been green lacewing larvaerelatively little research on releas-ing natural enemies in gardens and predatory miteslandscapes. Releases are unlikely toprovide satisfactory pest control inmost situations. Some marketed nat-ural enemies are not effective. Pray-ing mantids, often sold as egg cases,make fascinating pets. But mantidsare cannibalistic and feed indiscrimi-nately on pest and beneficial species.Releasing mantids does not controlpests. 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 toOnly a few natural enemies can be controlling pest B. economically damaging levels.effectively augmented in gardens andlandscapes. 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 butand perhaps a few other species. For become excessively abundant and cause damage when pesticides applied againstexample, 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 lacewingbulk 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. ◆ 5 of 7 ◆
October 2007 Biological Control and Natural EnemiesHandbook and Pests of Landscape Trees control. Natural enemies that do not WORLD WIDE WEB SITESand 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.cornellever possible. versely, a parasite or predator with .edu/ent/biocontrol multiple annual generations, that canIs 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/biocontrolhuman health and the environ- moderate, will likely be a more effec-ment. Most negative impacts from tive natural enemy. Biological Control News, Midwestexotic 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.htmlcarrying 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/bioconby poorly conceived importations Univ. Calif. Div. Agric. Nat. Res. Publ.of predatory vertebrates like mon- 3386. Oakland. UC Statewide IPM Program Naturalgooses. 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.ipmcal control. To avoid these problems, and J. H. Klotz. Oakland. Univ. Calif. .ucdavis.edu/PMG/NE/index.html vbiological 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 orHelp 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) 643-5470Do not bring uncertified fruit, plants, Calif. Agric. Nat. Res. Publ. 7487. Also • http://anrcatalog.ucdavis.eduor soil into California. Take unfamil- available online, http://www.ipmiar pests to your county agricultural .ucdavis.edu/PMG/menu.invertebratecommissioner or Cooperative Exten- .htmlsion 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.htmlpest insects or mites, not all can berelied 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.htmlscales. 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, andsuch 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 andenvironmental requirements of thepest and natural enemy also deter-mine the effectiveness of biological ◆ 6 of 7 ◆
October 2007 Biological Control and Natural EnemiesFor more information contact the Universityof California Cooperative Extension in yourcounty. See your telephone directory foraddresses and phone numbers.AUTHOR: S. H. Dreistadt, UC Statewide IPMProgram, DavisTECHNICAL EDITOR: M. L. FlintCOORDINATION & PRODUCTION: P. N. GalinILLUSTRATIONS: 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 CelesteGreen 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 predatoryenemy 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 ValleyGrape Vineyards. Oakland. Univ. Calif. Div.Agric. Nat. Res. Leaflet 21530; predatorymite: 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 CHEMICALSProduced by UC Statewide IPM Program, Pesticides are poisonous. Always read and carefully follow all precautions and safety recommendationsUniversity 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 peerreviewed 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- color, national origin, religion, sex, gender identity, pregnancy (including childbirth, and medical condi-als. This review process was managed by the ANR tions related to pregnancy or childbirth), physical or mental disability, medical condition (cancer-relatedAssociate 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, Vietnamhave 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. Universitythat are not mentioned. policy is intended to be consistent with the provisions of applicable State and Federal laws. Inquiries 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) 987-0096Integrated Pest Management. ◆ 7 of 7 ◆