Introduction

Biological control (or biocontrol) is a key component in establishing an ecological and integrated approach to pest management. We define biological control as “the decline in pest density as a result of the presence of natural enemies.” The degree of pest decline might result in partial or complete pest suppression. We use the terms “natural enemies,” “beneficials,” and “biocontrol agents” synonymously to refer to predators, parasites (or parasitoids), and diseases of pests.

Normally, natural enemies reproduce on their own and are self-sustaining, 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. Specialist natural enemies (such as most parasitic wasps which lay an eggs inside the body of its host and their larvae feed on the host’s tissues, eventually killing the host) depend on one or a few food choices and usually increase and decline with the pest population (after a certain lag period). 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.

Insect pests are also susceptible to entomopathogenic nematodes (roundworms) and a variety of diseases caused by pathogens, and 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).

Natural enemies can be disrupted by chemicals, can struggle in poor habitat with low pest numbers, are in some cases difficult to sample, and may be incapable by themselves of suppressing pests below damage thresholds.

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

One must know that biological control agents can have unanticipated effects that include attacking beneficial and native species. Additionally, new organisms could bring in new diseases and hyperparasites that could negatively affect biocontrol agents that are already present and in use. Because of this, we ask that you use caution when acquiring biocontrol agents from outside the state and check with the Oregon Department of Agriculture to see if the species is approved

Classical biological control

Classical biological control is the importation of natural enemies for release and permanent establishment in a new region. In the Pacific Northwest, we have had very few cases of highly successful classical biocontrol in agriculture. One successful biocontrol agent, the filbert aphid parasite (Trioxys pallidus), was imported from Europe and introduced (in small numbers) by OSU scientists in the mid-1980s. Since then, this tiny wasp has spread throughout the growing region and increasingly maintains the filbert aphid below treatment thresholds. In another case, the spread of and damage by the apple ermine moth (Yponomeuta malinellus), has been greatly reduced by the successful introduction of a wasp parasite (Ageniaspis fuscicollis) in the late 1990s. A cooperative biocontrol program among USDA-APHIS, ODA, and OSU for cereal leaf beetle began in 2000 and was considered successful by 2010. The establishment of the larval parasitoid, Tetrastichus julis (Eulophidae), yielded control below thresholds in some regions of the PNW, especially when combined with altered cultural practices (tillage, irrigation, crop rotation, etc.) and pesticide application. In some cases, 100% parasitism was achieved. An egg-larval parasitoid, Ascogaster quadridentatus (Braconidae) was introduced to help manage codling moth, a key pest of apple and pear. Economic success of this introduction is unknown; however, recovery of this parasitoid from codling moth has been reported.

Ongoing PNW classical biocontrol efforts include 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) and brown marmorated stink bug (BMSB), were initiated in 2011.

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 within minutes. If biocontrol agents are native, then a release can be directed to augment and improve the rate of natural colonization and control. If the natural enemy is non-native, then overwintering success is not expected, and only in-season benefits will occur. 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 greatly 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. Many pests are “secondary pests” in that they only reach economic pest levels when their natural enemies are disrupted by pesticides intended to control a different species. Using least toxic and selective controls over broad-spectrum compounds (such as most organophosphates, carbamates, and pyrethroids) can often prevent secondary pest outbreaks. Two database listings of pesticide effects on beneficial organisms are:
  • http://www.enhancedbiocontrol.org
  • http://utahpests.usu.edu/ipm/htm/fruits/home-orchard-guide/toxicity-pest…
• 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 poorly 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. 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. As 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 selecting 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 natural enemies within and surrounding the crop.

Resources for implementation of biological control

The Association of Natural Biocontrol Producers (ANBP is a professional association representing the biological pest management industry). Web: http://www.anbp.org/

The IPM Practitioner’s 2013 Directory of Least Toxic Pest Control Products. An annual (Nov.-Dec. issue), 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, PO Box 7414, Berkeley, CA 94707; tel 510-524-2567; $15.00 includes postage and handling ( http://www.birc.org/ E-mail: birc@igc.org)

A great video on habitat and biological control that was recently made in 2015 by Eric Brennan, PhD researcher at USDA in Salinas, that features the Dan Karp article “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 (https://www.youtube.com/watch?v=zLvJLHERYJI )

Harpinder, S., S. Wratten, R. Costanza, J. Pretty, J. R. Porter, and J. Reganold. 2015. Significance and value of non-traded ecosystem services on farmland. PeerJ 3:e762; DOI 10.7717/peerj.762 ( https://peerj.com/articles/762.pdf )

Oregon Department of Agriculture provides a list of invertebrates approved for importation into Oregon at: ( http://www.oregon.gov/ODA/PLANT/IPPM/Pages/appr_insects.aspx )

Except as otherwise provided in rules of the ODA, invertebrate species listed in this list may be imported, possessed, sold, purchased, exchanged or transported within the state without an ODA permit. A permit for the importation, possession, or intrastate transportation of ODA-approved species may be required by the US Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine, Form 526.

Suppliers of Beneficial Organisms in North America provides a list of commercial suppliers and beneficial organisms used for biological control. Last updated in 1997, the list is provided for reference purposes only. Contact Dept. of Pesticide Regulation, 830 K St., Sacramento, CA 95814; phone: 916-324-4264. No charge. (http://www.cdpr.ca.gov/docs/pestmgt/ipminov/bensuppl.htm )

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 ( http://www.xerces.org/ )

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?

References

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.

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.