Biological Control

Leonard Coop, David Lowenstein, and Joshua Vlach
March 2019



Biocontrol is generally more compatible with organic and sustainable agricultural approaches and less compatible with pesticide-dependent agriculture, especially when the less selective, more broad-spectrum chemistries are used. Biocontrol agents tend to be highly susceptible to non-selective pesticides and so pests that are normally controlled by natural enemies can be released from suppression due to short and medium-term pesticide effects. The term “secondary pest outbreaks” is used when this scenario occurs. This reduction in natural enemies can also produce dependence on further pesticide usage and result in a hard-to-break cycle of chemical dependency.

Ideally, natural enemies reproduce on their own and are self-sustaining, are compatible in combination with other integrated control tactics, and are not harmful to other aspects of the ecosystem. Generalist natural enemies (such as most aphid predators) can switch readily among alternative food sources. Thus, when pest numbers are low, the generalist natural enemies may maintain population numbers by consuming other prey species. Specialist natural enemies (such as most parasitoid wasps) depend on one or more food choices and usually increase and decline with the pest population (after a certain lag period). Natural enemies can be disrupted by chemicals, can struggle in poor habitat with low pest numbers, are in some cases difficult to sample or even detect (and thus can be undervalued as to their benefits), and may be incapable by themselves of suppressing pests below damage thresholds.

Insect pests are also susceptible to entomopathogenic nematodes (roundworms) and a variety of diseases caused by pathogens, which include viruses, bacteria, fungi, and protozoa. Natural populations of insect pests are commonly attacked by pathogens, and some pathogens have been mass-produced and are used as biocontrol agents (e.g., microbial insecticides).

Thus, natural enemies, especially a combination of generalists and specialists, can be an extremely useful part of pest management programs that recognize and encourage their activity. At the same time, one must keep in mind that biological control agents can have unanticipated effects that include attacking beneficial and native species. New biocontrol agents increasingly require long-term, stringent evaluations in quarantine for non-target effects and efficacy in controlling the target pest before release. Biocontrol agents that are candidates for introduction may be rejected if, in addition to the target species, they attack native non-pest species. Another risk of introducing new biocontrol agents is the risk of host shifting, which is an unexpected change of attacking the pest (host) despite previous efforts to determine host range.

Types of biological control

In addition to the philosophy of “doing nothing” in order to allow natural biological control to work, there are three principal approaches involving human activity:

  1. Classical biological control
  2. Augmentative biological control
  3. Conservation biological control

Classical biological control


Previous PNW classical biocontrol efforts included programs directed at Russian wheat aphid, orchard leafrollers, larch casebearer, and cherry bark tortrix. Searches for biological control agents for two new invasive pests—spotted-wing drosophila (SWD, Drosophila suzukii) and brown marmorated stink bug (BMSB, Hyalomorpha halys)—were initiated in 2011. Several wasps were imported from Korea for quarantine, testing, and potential release against SWD. The BMSB egg parasitioid, Trissolcus japonicus, was found established outdoors in Vancouver, Washington in 2015 and Portland, Oregon in 2016 and has been detected yearly in both areas. As a result of this finding, experimental releases of the parasitoid have begun in Oregon.

Augmentative biological control

Augmentative or supplemental biological control typically involves the mass-production and repeated releases of natural enemies. This approach is used most often for slow-moving pests such as mites and aphids, in enclosed spaces such as greenhouses, by home gardeners, and in organic agriculture where few disruptive chemicals are used. The dispersal capability of the natural enemy should be taken into consideration when matching a natural enemy for control of the pest. For example, many homeowners have wasted money using ladybug adults to control aphids, only to see them disperse away within minutes. If biocontrol agents are native or established from exotic sources, then a release can be directed to augment and improve the rate of natural colonization and control. If the biocontrol agent is non-native and overwintering success is not expected, only in-season benefits will occur. It was demonstrated in Oregon strawberries during the mid-1990s that the PNW-native predatory mite Neoseiulus fallacis can be purchased from insectaries and released in the early fall to re-establish healthy populations that normally control the twospotted spider mite, in cases where pesticides had previously been used to control root weevils (Croft and Coop 1998). Some other predator mite species, such as N. californicus, which may be more readily available for purchase than is N. fallacis, may provide in-season control but may not survive the relatively colder winters that N. fallacis is adapted to survive. Since natural enemies are all specialized to some degree, it’s important to know the pest and which agent(s) are appropriate for the given situation. Table 1 lists some target pests commonly found in home garden and agricultural systems and the associated commercially-available beneficial organisms. Steps for acquisition and release of biocontrol agents must be planned carefully and followed. Release guidelines depend on an understanding of the biology of the pest, the natural enemy, and the influence of the host plant on both. Conservation efforts (below) can in some cases enhance the outcome of augmented biocontrol agents.

Conservation biological control

Conservation biological control refers to the manipulation and/or protection of habitat and resources to support and encourage natural enemies in order to increase their numbers and effectiveness. This may include the use and encouragement of the natural enemies’ needs, such as nectar and pollen, alternative hosts, and certain types of non-disrupted habitat. These resources all can potentially enhance the fecundity, longevity, and survival of natural enemies.

Some tactics for conservation biological control include:

  • Careful use of pesticides and tillage to avoid disturbing natural enemies. There are secondary pests that only reach economic pest levels when their natural enemies are disrupted by pesticides, that were applied in order to control a different species. Using least toxic and selective controls in the place of broad-spectrum compounds (such as most organophosphates, carbamates, and pyrethroids) can help prevent secondary pest outbreaks. Online databases and listing of pesticide effects on beneficial organisms include:
  • Non-crop plantings in or around the crop field that may provide shelter, alternative prey, nectar, and pollen. Table 2 gives some examples of flowering plants that are visited by natural enemies.
  • Food sprays (such as yeast and sugar sprays) to attract parasitoid wasps, lady beetles, lacewings, and hoverflies.
  • Manipulating crop and non-crop architecture in ways that improve natural enemy activities (for example, using wind-break plantings as a barrier to prevent dry, dusty conditions favorable to pest mite flare-ups. Predatory mites need sufficient humidity and can be inhibited by such conditions.)

The effects of the above tactics are not well understood, and they can be less consistent than other forms of biological control due to the complex interactions involved. However, they do make use of the local natural beneficial species already present in the landscape. Note also that conservation biological control efforts can enhance natural enemies released in classical and augmentative biological control programs. For example, some of the most commonly used methods for providing floral resources (e.g. pollen, nectar, nectaries), also known as beneficial “insectary plantings,” include:

  1. Planting within the crop field in strips or smaller blocks
  2. Using perennial and annual border plantings
  3. Planting within hedgerows
  4. Establishing cover crops
  5. Careful management of flowering weeds

Coincidentally, these insectary planting methods also can provide habitat and alternate hosts for natural enemies in certain situations. Shelter and alternate hosts also can be supported through methods such as careful rotation, alternate row harvest, and “beetle banks,” which are graded low banks of dense grasses placed within the field or in fence row corridors inhabited by appropriate vegetation.

Just as when selecting any new crop management method, choosing insectary plantings for conservation biological control should include consideration of numerous biological, agronomic, and economic factors. Table 3 gives an example of the range of factors to consider in designing an insectary planting. To justify the continued use of an insectary planting, the on-site assessment should consider the same factors as the preliminary selection process, as well as a sampling of pests and beneficials within and surrounding the crop.

Resources for implementation of biological control

The IPM Practitioner’s 2015 Directory of Least Toxic Pest Control Products. A regularly updated, comprehensive, statewide listing of biological control agents and other “least toxic” pest control products for a variety of agricultural, urban, and domestic uses, and their producers and distributors. Bio-Integral Resource Center

An informative 12 minute video on habitat and biological control made in 2015 by Eric Brennan, PhD researcher at USDA in Salinas, CA, that features the article by Dan Karp, “Co-managing fresh produce for nature conservation and food safety,” recently published by the National Academy of Sciences: Biological Control Buffet in the Salad Bowl of America



The Xerces Society. A nonprofit organization formed in 1971 which protects wildlife through the conservation of invertebrates and their habitat. Their focus has expanded beyond native pollinators to include all invertebrates including other native species, predators, and parasitoids. They have programs to document the impacts of pesticides on invertebrates including biocontrol agents. Xerces has resources to provide education and training on conservation biological control and are very active in the Pacific Northwest. 628 NE Broadway Ste 200, Portland OR 97232 USA; tel: 855-232-6639

Considerations for incorporating insectary plantings to sustain natural enemies

Timing of flowering

  1. Will the floral resources be present when needed?
  2. Will the flowers attract natural enemies to or away from the target pest at certain times?

Characteristics of the natural enemies

  1. What are the relative preferences that key natural enemy and pest species have for the different flowers?
  2. What are the different requirements for nectar, pollen, shelter, and alternate host food among these key species?
  3. What are the relative foraging ranges and dispersal abilities of these key species?

Agronomic considerations

  1. How competitive are the plantings with the crop or other weeds?
  2. Do the plantings have the potential to harbor weeds or be weeds themselves?
  3. Can the plantings serve as an alternate host for crop disease?
  4. Are the plants toxic to any livestock or other local animals?

Economic and management considerations

  1. Can the planting be harvested as an additional crop?
  2. What are the costs of seed, establishment, and maintenance?
  3. How do these costs compare to other management options?
  4. Are the plantings compatible with the main pest management plan?


Bradley, F.M, B.W. Ellis, D.L. Martin. 2010. The Organic Gardener’s Handbook of Natural Pest and Disease Control: A Complete Guide to Maintaining a Healthy Garden and Yard the Earth-Friendly Way. Rodale Organic Gardening Books. Rodale Press (Emmaus, PA).

Bugg, R.L. and C. Waddington. 1994. “Using Cover Crops to Manage Arthropod Pests of Orchards: A Review.” Agriculture, Ecosystems Environment. Vol. 50, pp. 11–28.

Bugg, Robert L. Feb. 1994. “Beneficial Insects and their Associations with Trees, Shrubs, Cover Crops, and Weeds.” Sustainable Ag Research & Education Program. University of California at Davis 95616.

Colley, Micaela R. 1998. Enhancement of Biological Control with Beneficial Insectary Plantings. Oregon State Univ. Masters Thesis.

Croft, B.A. and L.B. Coop. 1998. “Heat units, release rate, prey density, and plant age effects on dispersal by Neoseiulus fallacis (Acari: Phytoseiidae) after inoculation into strawberry.” Journal of Economic Entomology 91:94-100. Access online via:

Flint, M.L, S.H. Driestadt and J.K. Clark. 1999. Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control. UC Div. Of Agric. And Nat. Resources. Univ. California Press.

Hajek, Ann E. 2004. Natural Enemies: An Introduction to Biological Control. Cambridge University Press.

Long, R.F., A. Corbett, L. Lamb, C.R. Horton, J. Chandler, M. Stimmann. 1998. “Beneficial Insects Move from Flowering Plants to Nearby Crops.” California Agriculture. Sept-Oct. issue.

Maltas, Michael. 1994. Organic Ag Advisors—Plants for Beneficial Insect Habitat. PO Box 1622, Colfax, CA 95713.

Merril, Richard. 1995. “Beneficial Insectary Plantings.” Shepherd’s Garden Seeds Newsletter. California.

Pickett, C.H. and R.L. Bugg. 1998. Enhancing Biological Control: Habitat Management to Promote Natural Enemies of Agricultural Pests. Univ. of California Press, Berkeley, CA.

Reynolds, William. 1994. “Attracting Beneficial Insects to the Farm Field.” Grower—New England Vegetable & Small Fruit Newsletter. Vol 94–7. Eastern Rhode Island Cooperative Extension.

The Xerces Society. 2014. Farming with Native Beneficial Insects: Ecological Pest Control Solutions. Storey Publishing.



(See also soft-bodied arthropods)

predatory midge

Aphidoletes aphidimyza

parasitoid wasp


big-eyed bug

Geocoris pallens

lady beetle (“ladybug”)

Hippodamia convergens


Chrysoperla downesi, C. plorabunda, C. rufilabris

minute pirate bug

Orius insidiosus, O. minutus, O. tristicolor


(See also Butterfly and moth)

braconid parasitoid wasp

Chelonus insularis

Black fly larvae

bacterial endotoxin (Bti)



parasitoid wasp

Bracon hebeter


viral pathogen

Nuclear polyhedrosis virus (NPV)

bacterial endotoxin (Btk, Bta)


parasitoid wasps of eggs

Trichogramma minutum, T. pretiosum, T. platneri

Codling moth larvae

granulosis virus pathogen

Baculovirus carpocapsae


parasitic nematode

Steinernema carpocapsae, S. feltiae

Fly (garbage- and manure-breeding)

parasitoids of puparia


histerid beetle predator

Carcinops pumilio

Fungus gnat (larvae)

predatory mite

Hypoaspis miles, H. aculeifer

parasitic nematode

Heterorhabditis megidis,

Steinernema carpocapsae, S. feltiae

bacterial endotoxin (Bti)

Bacillus thuringiensis var. israelensis

Grasshopper (nymphs and adults)


Nosema locustae


parasitic nematodes of larvae



braconid parasitoid of larvae

Dacnusa sibirica


lady beetle (“mealybug destroyer”)

Cryptolaemus montrouzieri

Mite: twospotted spider (Tetranychus urticae)

predatory mite


predatory six-spotted thrips

Scolothrips sexmaculatus

minute pirate bug

Orius minutus, O. tristicolor

big-eyed bug

Geocoris pallens

Mosquito larvae

predatory fish


bacterial endotoxin (Bti)



lady beetle

Chilocorus fraternus


parasitoid wasp

Metaphycus helvolus


lacewing larvae (in larval stage)

Chrysoperla downesi, C. plorabunda, C. rufilabris

fungal pathogen

Beauveria bassiana

lady beetle

Chilocorus fraternus, Hippodamia convergens

pirate bug

Orius minutis, O. tristicolor

predatory thrips

Scolothrips sexmaculatus

Thrips larvae (See also soft-bodied arthropods)

predatory mite



Chrysoperla downesi, C. plorabunda, C. rufilabris

minute pirate bug

Orius minutus, O. tristicolor

Wax moth larvae (in honeycombs)

bacterial endotoxin (Bta)

Bacillus thuringiensis var. aizawai (e.g. Certan)

Weevil in landscape plants

parasitoid wasps of larvae

Anisopteromalus calandrae

parasitic nematode


Whitefly nymph (See also soft-bodied arthropods)

parasitoid wasps of eggs

Encarsia formosa, Eretmocerus californicus











Common name (botanical name)

Beneficial insects

Apiaceae (Carrot family)

Angelica (Angelica)

lady beetle (“ladybugs”), lacewing

Anise (Pimpinella anisum)

parasitoid wasp

Blue lace (Trachymene caerulea)

parasitoid wasp

Caraway (Carum caryi)


Chervil (Anthriscus cerefolium)

parasitoid wasp

Coriander (Coriandrum sativum)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Dill (Anethum graveolens)

hoverfly, lady beetle, parasitoid wasp

Fennel (Foeniculum vulgare)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Lovage (Lovisticum officinale)

parasitoid wasp

White lace flower (Ammi majus)


Wild carrot (Daucus carota)

hoverfly, predatory bug, lady beetle, lacewing, parasitoid wasp

Asteraceae (Daisy family)

Blazing star, gayfeather (Liatrus spp.)

minute pirate bug, big-eyed bug, parasitoid wasp

Chamomile (Anthemis nobilis)

lady beetle

Cosmos (Cosmos bipinnatus)

hoverfly, lacewing, minute pirate bug

Golden marguerite (Anthemis tinctoria)

lady beetle, parasitoid wasp, parasitoid tachinid fly

Goldenrod (Solidago altissima)

soldier beetle, predatory bug, lady beetle, parasitoid wasp

Marigolds, signet (Tagetes tenuifolia)

minute pirate bug, parasitoid wasp

Mexican sunflower (Tithonia tagetifolia)

hoverfly, minute pirate bug

Sunflower (Helianthus annuus and H. debilis)

hoverfly, lady beetle, parasitoid wasp

Tansy (Tanecetum)

hoverfly, lady beetle larvae, parasitoid wasp

Yarrow, milfoil (Achillea millefolium)

hoverfly, parasitoid wasp


hoverfly, parasitoid wasp

Brassicaceae (Cabbage family)

Broccoli (Brassica oleracea)

hoverfly, parasitoid wasp

Sweet alyssum (Lobularia maritima)

hoverfly, parasitoid wasp, parasitoid tachinid fly

Globe candytuft (Iberis umbellata)


Mustards (Brassica hirta and B. juncea)

hoverfly, minute pirate bug, big-eyed bug

Dipsaceae (Scabiosa family)

Cephalaria (Cephalaria giganitica)

hoverfly, parasitoid wasp

Dipsacus (Dipsacus spp.)


Pincushion flower (Scabiosa caucasica)

hoverfly, parasitoid wasp

Scabiosa (Scabiosa atropurpurea)


Fabaceae (Legume family)

Alfalfa (Medicago sativa)

bee, predatory bug, lacewing, lady beetle, parasitoid wasp

Clover (Trifolium spp.)

bee, predatory bug, lacewing, lady beetle

Vetch (Vicia spp.)

bee, predatory bug, lacewing, lady beetle

Hydrophyllaceae (Waterleaf family)

Fiddleneck/Phacelia (Phacelia tanacetifolia)

bee, predatory bug, hoverfly

Lamiaceae (Mint family)

Germander (Teucrium spp.)

bee, parasitoid wasp

Polygonaceae (Buckwheat family)

Buckwheat (Eriogonum spp. and Fagopyrum spp.)


See notes for Table 1.