Consumers are becoming more concerned about pesticide usage on ornamental plants and turfgrass in and around their homes and on the fruits and vegetables they eat. Not only are the negative health and environmental risks of pesticides of concern but also the impacts of neonicotinoids and other broad-spectrum pesticides on pollinators and other beneficial organisms. Growers and green industry professionals are searching for alternative pest management tactics to satisfy consumer demands and the desire for sustainability and operational flexibility. Many are considering biological control. The benefits of biological control include reduced reliance on pesticides, decreased potential for development of pesticide resistance, flexibility in usage of personal protective equipment, shorter (or no) restricted entry intervals, and reputational benefit of being a sustainable and responsible grower or professional. Biological control can also be used to manage pest populations that have developed pesticide resistance. This publication provides an introduction to biological control and explains how to integrate biological control into an integrated pest management (IPM) program. For the purposes of this publication, pests are defined as any undesirable insect, mite, plant (weed), or organism that causes disease (pathogen) or damage on ornamental plants, turfgrasses, fruits, and vegetables.
What is Biological Control?
In nature, organism populations suffer frequent attacks and high mortality rates from predators, parasites, parasitoids, and diseases, collectively called “natural enemies.” Biological control tactics use natural enemies or agents (some practitioners call them “beneficials”) to manage pests. The ultimate goal of biological control is to suppress pest population and damage without pesticide or with reduced pesticide use. Natural enemies are utilized differently depending on the target pest, host, environmental condition, and pest life cycle. There are three general approaches to biological control.
Classical Biological Control
Classical biological control refers to the practice of introducing one or a group of natural enemy species of foreign origin to control a pest that many times is also foreign in origin (called exotic, introduced, or invasive).1 Often, the natural enemies are found in the home range of the invasive pest. Some notable examples of classical biological control include the use of decapitating flies (several Pseudacteon species) against red imported fire ants, and a group of flea beetles, thrips, and stem borers used against alligator weed. Because of the long, rigorous, and costly process of finding, testing, quarantining, and rearing these natural enemies, classical biological control programs are typically conducted by scientists at governmental agencies or universities with public funding. Modern classical biological control programs mandate extensive testing of the natural enemy host ranges before introduction so that the selected natural enemies attack only the intended target pest and do not cause harm to other non-target organisms. Once released into the environment, these selected natural enemies spread and manage the pest population with minimal assistance and intervention from the practitioners. The practical application of classical biological control by growers, professionals, and consumers on ornamental plants, turfgrasses, fruits, and vegetables is minimal.
Fortuitous or adventive biological control is a variant of classical biological control where natural enemies arrive from elsewhere by their own means and control the exotic pest population.2 These adventive natural enemies may have arrived with the pest or at a later time without introduction. There are also incidences where native natural enemies switch to using invasive pests as food or host on their own.
Augmentative Biological Control
Augmentative biological control refers to the practice of releasing biological control agents (often mass-reared in insectaries) into an area where natural enemies are not present or present at a number too low to suppress a pest population.3 The goal of augmentative biological control is to increase the number or the effectiveness of natural enemies in an area to a level high enough to control the pest population. This type of biological control is most often practiced in greenhouses, nurseries, and some fruit and vegetable fields. The mass-produced biological control agents are purchased from the suppliers and released/applied en masse into the infested area to kill the pests. Biological control agents mass-produced by insectaries are often host-specific (i.e., they only attack one or two kinds of pests). Therefore, practitioners need to identify the pest species accurately so that the correct natural enemy species can be purchased for release. Depending on the pest and biological control agent species, as well as the environment and production practices, augmentative biological control can be achieved through inoculative releases or inundative releases. In inoculative releases, the biological control agents are released in small numbers to establish a population that provides long-term and sustained suppression of the pest population. In inundative releases, the biological control agents are released in large numbers to quickly overwhelm the pest population without the expectation of propagating the biological control agent population or continuing the suppression of the pest population.
Conservation Biological Control
Conservation biological control refers to a collection of methods and approaches in manipulating the habitat, plant diversity, production practice, and pest management practice to increase the population and effectiveness of natural enemies.4 An area with more complex and diverse plant and animal communities is known to have a greater diversity of natural enemies and a lower abundance of pests. Conservation biological control practitioners often start with manipulating the farmscape or landscape, such as growing insectary plants (i.e., plant species that can attract and retain natural enemies or provide natural enemies with food and shelter). Natural enemy diversity, abundance, and effectiveness increase as plant diversity and resources provided increase. Other conservation biological control practices seek to minimize impacts of habitat manipulation or farming practices on natural enemies. For example, growers or landscape care professionals may use mulch to provide shelters for ground beetles, or reduce pesticide use, or use pesticides that have minimal impacts on the natural enemies (i.e., compatible pesticides).
Biological control is a complex pest management strategy that requires a comprehensive understanding of the ecology and behavior of pests and natural enemies. As a result, biological control is often more difficult to design and put into action than simply spraying pesticides (chemical control). Biological control can sometimes be more expensive than conventional chemical control. When designed and implemented correctly, however, the benefits of biological control in terms of environmental sustainability, efficacy, and cost-effectiveness can outweigh these shortcomings.
Types of Biological Control Agents
Natural enemies of insects and mites generally fall into four different types, or guilds, based on how they utilize their prey or hosts: predators, parasites, parasitoids, and pathogens. Predators are organisms that feed on the target pests and include insects such as lady beetles, green lacewings, rove beetles, hover flies, and predatory mites (table 1). Parasites and parasitoids are interchangeable terms for some practitioners, but there are significant differences between the two types. Typically, parasites are microorganisms that live, feed, and lay eggs on or in a host without killing it. Parasitoids do the same as parasites but eventually kill the host. Parasitoids are typically parasitic insects such as tachinid flies or parasitic wasps (table 1). Pathogens include microorganisms, such as fungi, bacteria, nematodes, and viruses that cause diseases in pests. Pathogens that are used against insects and mites are referred to as “entomopathogenic.”
Natural enemies of plant pathogens are generally microorganisms similar to their targets (i.e., fungi, viruses, and bacteria). These microorganisms interact with plant pathogens in four primary ways: competition, hyperparasitism, induced resistance, and production of antimicrobial compounds.5 Competition is relatively straightforward. A large number of beneficial microorganisms is applied to the environment, which takes up all the available living spaces or resources and denies occupancy by plant pathogens. Bacillus subtilis is a common example, where products containing this bacterium are applied to soil or soilless growing medium to out-compete root rot causing pathogens (table 2). Hyperparasitism occurs when a beneficial microorganism parasitizes and eventually kills a plant pathogen. Some beneficial microorganisms can induce or cause plants to produce defensive chemical compounds to fend off pathogens (i.e., resistance). Hyperparasitism and induced resistance are very specific interactions among plants, beneficial microorganisms and pathogens, but are not widely utilized commercially. Production of antimicrobial metabolites that stop growth or kill the pathogens is the most common way biological control is used for disease management. The beneficial microorganisms, often bacteria, are mass-reared in fermentation vessels to produce specific antimicrobial compounds, which are later extracted and used as antimicrobial pesticides. The beneficial microorganisms can also be applied to the plants. When the beneficial microorganisms die, their cells release the antimicrobial compounds onto the leaf surface, thus killing the pathogens nearby or protecting the leaf from infection. Once again, some B. subtilis products are examples of using antimicrobial compounds. These products are sometimes mixed with copper-based fungicides to enhance the effect.
While some biological control agents or beneficial microorganisms can feed or parasitize a large number of pest species, some are effective against only one or two species of pests. For example, the predatory mite Amblysieus swirskii can feed on thrips, whiteflies, broad mites, and spider mites, whereas another predatory mite, Phytoseiulus persimilis, only feeds on spider mites (table 1). Differences also occur within the same biological control agent species. For example, Bacillus thuringiensis subsp. kurstaki is effective only against caterpillars, but Bacillus thuringiensis subsp. galleriae is effective only against white grubs (table 1). Because the relationships between biological control agents and pests can be quite specific, accurate identification of the pest organism or disease (often to the species level) is crucial to selecting the correct biological control agent species and the success of the biological control program.
When biological control agents are introduced or released into an environment, their application methods differ among species. Larger agents (sometimes referred to as “macro biological control agents”), such as predatory mites and parasitoids, are applied in loose carrier (usually bran), sachets, or cards adhered with eggs or pupae. Microbial biological control agents (sometimes referred to as “micro biological control agents”) are often diluted in water and sprayed onto the plants or drenched onto medium or soil.
Biological Control as Part of an IPM Program
No pest management tactic acts independently in an IPM program. The same principle applies to biological control tactics. For example, pest species must be accurately identified to select the correct biological control agents or microbial products. Also, biological control is most effective against a small pest population or when pesticides that can negatively impact the survival and functions of the biological control agents are removed from the program. Biological control must be an integral part of an IPM program, where biological control tactics are adopted in consideration of other tactics within the program and vice versa.6
An IPM program starts with scouting. In an IPM program that incorporates biological control, both the pest and natural enemy populations must be sampled, and their densities or abundance determined. Biological control performs more effectively when biological control tactics are applied when the pest population is still small. The release of biological control agents does not signal the end of scouting but a need for continuation so that other pest management tactics can be applied when the need arises. Successful biological control will suppress the pest population to a level that would not cause damage, and therefore, pesticide use can be delayed or avoided completely. However, when the pest population increases above the economic or aesthetic threshold, or the biological control agent population or effectiveness decreases, pesticides may have to be applied to suppress the pest population and damage and allow biological control to catch up.
Cultural and production practices that growers employ may also impact biological control. There are often more natural enemies and greater biological control effectiveness when the fields or landscapes contain more abundant and diverse vegetation. Growers and landscape designers should strive to practice environmental engineering or production practices that incorporate many plant species, particularly those that can provide resources to the biological control agents. Intercropping and cover cropping with insectary plants help attract and retain biological control agents and serve to reduce weed management needs and costs, improve soil health, and control soil erosion. Maintaining vegetation and mulch/debris allows biological control agents to find refuge and resources and maintain a consistent ever-present population that can disperse as pest management needs arise.
Which pesticides are used, and how and when, has a significant impact on the success of biological control. Biological control agents are as susceptible as, and in some cases, more sensitive to pesticides than their target pests or diseases. Broad-spectrum pesticides can kill or affect a wide variety of biological control agents. For example, organophosphate and pyrethroid insecticides are very toxic to many biological control agents and pollinators, and fungicides that target multiple sites (such as copper and mancozeb) can reduce the effectiveness of beneficial microorganisms. These pesticides should not be used in conjunction with biological control. Instead, pesticides that have a reduced risk or lower toxicity to the biological control agents (commonly referred to as the compatible pesticides) should be used. Additionally, some pesticides may also destroy habitats of the biological control agents and should not be used. For example, the use of broad-spectrum herbicides and other indiscriminate weed management practices must be eliminated or carefully considered if companion plants are used. How pesticides are applied also impacts the success of biological control. Application methods (such as drench) and timing (depending on the biological control agents) that avoid direct contact or leave behind large amounts of residue on the plant surface should be used.
Biological control is a knowledge-intensive strategy of pest management. Successful implementation of a biological control program requires a thorough understanding of the pests, the natural enemies, their environment (including other pest management practices), and the interactions of all factors. Success is often achieved after many considerations, modifications of current production, and pest management practices, as well as trial-and-error. Despite being challenging to adopt, biological control and IPM, in general, create benefits that contribute to building a sustainable environment and increasing profitability by reducing management inputs.
Table 1. Commercially available biological control agents for major arthropod pests.7
| Types | Species | Commonly known as | Target insects and mites |
| Predatory mite | Amblydromalus limonicus | Limonicus mite | Thrips, whitefly |
| Predatory mite | Amblyseius andersoni | Andersoni mite | Twospotted spider mite, russet mite, rust mite, broad mite |
| Predatory mite | Amblyseius degenerans | Degenerans mite | Thrips, broad mite, twospotted spider mite |
| Predatory mite | Amblyseius swirskii | Swirskii mite | Thrips, whitefly, and broad mite |
| Predatory mite | Galendromus occidentalis | Galendromas mite | Twospotted spider mite, errophyid mite, russet mite |
| Predatory mite | Mesoseiulus longipes (formerly Phytoseiulus longipes) | Longipes mite | Twospotted spider mite |
| Predatory mite | Neoseiulus californicus (formerly Amblyseius californicus) | Californicus mite | Twospotted spider mite, broad mite, cyclamen mite |
| Predatory mite | Neoseiulus cucumeris (formerly Amblyseius cucumeris) | Cucumeris mite | Thrips, fungus gnat, twospotted spider mite, tarsonemid mite |
| Predatory mite | Neoseiulus fallacis (formerly Amblyseius fallacis) | Fallacis mite | Twospotted spider mite, European red mite, citrus red mite |
| Predatory mite | Phytoseiulus persimilis | Persimilis mite | Twospotted spider mite |
| Predatory mite | Stratiolaelaps scimitus (formerly Hypoaspis miles) | Hypoaspis mite | Fungus gnat larva, thrips pupa |
| Predatory beetle | Adalia bipunctata | Ladybird beetle | Aphid |
| Predatory beetle | Dalotia coriaria (formerly Atheta coriaria) | Rove beetle | Thrips, fungus gnat |
| Predatory beetle | Cryptolaemus montrouzieri | Mealybug destroyer | Mealybug, soft scale |
| Predatory beetle | Cybocephalus nipponicus | Cybocephalus | Armored scale |
| Predatory beetle | Delphastus catalinae | Delphastus | Whitefly |
| Predatory beetle | Hippodamia convergen | Ladybird beetle | Aphid |
| Predatory beetle | Rhyzobius lopanthae | Lindorus | Armored scale, soft scale, mealybug |
| Predatory beetle | Stethorus punctillum | Spider mite destroyer | Twospotted spider mite |
| Lacewings | Chrysoperla spp. | Green lacewing | Aphid, mealybug, whitefly |
| Lacewings | Micromus variegatus | Brown lacewing | Aphid, whitefly, mealybug |
| Lacewings | Sympherobius barberi | Brown lacewing | Aphid, thrips, whitefly, spider mite, small caterpillar, leafhopper |
| Predatory flies | Aphidoletes aphidimyza | Predatory midge | Aphid |
| Predatory flies | Feltiella acarisuga | Predatory midge | Spider mite |
| Predatory thrips | Scolothrips sexmaculatus | Scolothrips | Spider mite |
| Parasitic wasp (parasitoid) | Anagyrus vladimiri (formerly Anagyrus psedudococci) | Anagyrus | Citrus mealybug, grape mealybug |
| Parasitic wasp (parasitoid) | Aphelinus abdominalis | Abdominalis | Potato aphid |
| Parasitic wasp (parasitoid) | Aphidius colemani | Colemani | Cotton/melon aphid, green peach aphid, |
| Parasitic wasp (parasitoid) | Aphidius ervi | Ervi | Foxglove aphid, pea aphid, potato aphid |
| Parasitic wasp (parasitoid) | Aphidius matricariae | Matricariae | Green peach aphid |
| Parasitic wasp (parasitoid) | Aphytis melinus | Aphytis | Oleander scale, citrus scale |
| Parasitic wasp (parasitoid) | Dacnusa sibirica | Dacnusa | Leafminer |
| Parasitic wasp (parasitoid) | Diglyphus isaea | Diglyphus | Leafminer |
| Parasitic wasp (parasitoid) | Encarsia formosa | Encarsia | Greenhouse whitefly |
| Parasitic wasp (parasitoid) | Eretmocerus eremicus | Eretmocerus | Sweetpotato whitefly |
| Parasitic wasp (parasitoid) | Eretmocerus mundus | Mundus | Sweetpotato whitefly |
| Parasitic wasp (parasitoid) | Leptomastix dactylopii | Dactylopii | Mealybug |
| Parasitic wasp (parasitoid) | Pediobius foveolatus | Pediobius | Mexican bean beetle |
| Parasitic wasp (parasitoid) | Peristenus relictus | Peristenus | Lygus bug |
| Parasitic wasp (parasitoid) | Tamarixia radiata | Tamarixia | Asian citrus psyllid |
| Parasitic wasp (parasitoid) | Trichogramma brassicae | Trichogramma | Moth egg |
| Parasitic wasp (parasitoid) | Trichogramma minutum | Trichogramma | Moth egg (eastern U.S.) |
| Parasitic wasp (parasitoid) | Trichogramma ostriniae | Trichogramma | European corn borer |
| Parasitic wasp (parasitoid) | Trichogramma platneri | Trichogramma | Moth egg (western U.S.) |
| Parasitic wasp (parasitoid) | Trichogramma pretiosum | Trichogramma | Moth egg |
| Predatory true bug | Dicyphus hesperus | Dicyphus | Whitefly |
| Predatory true bug | Orius insidiosus | Minute pirate bug, insidious flower bug | Thrips, whitefly, aphid |
| Predatory true bug | Podisus maculiventris | Spined soldier bug | Colorado potato beetle, caterpillars |
| Predatory true bug | Zelus renardii | Assassin bug | Various (a generalist predator) |
| Entomopathogenic nematode | Heterorhabditis bacteriophora | Nemasys® G and others | White grub, Colorado potato beetle, black vine weevil |
| Entomopathogenic nematode | Heterorhabditis megidis | NemaSeek™ and others | Black vine weevil larva, soil-borne beetle larva |
| Entomopathogenic nematode | Steinernema carpocapsae | Millenium® and others | Chinch bug, armyworm, peach tree borer, and others. |
| Entomopathogenic nematode | Steinernema feltiae | Nemasys® and others | Thrips, fungus gnat |
| Entomopathogenic nematode | Steinernema kraussei | Nemasys® L | Black vine weevil |
| Entomopathogenic nematode | Steinernema riobrave | Nemasys® R and others | Mole cricket, root weevil, caterpillar |
| Entomopathogenic fungus | Beauveria bassiana | BotaniGard®, Mycotrol®, Velifer™, and others | Aphid, grub, chinch bug, grasshopper, cricket, sod webworm, leafhopper, whitefly, thrips |
| Entomopathogenic fungus | Hirsutella thompsonii | Hirsutella | Spider mite |
| Entomopathogenic fungus | Isaria fumosoroseus | Ancora®, Nofly WPTM, and others | Whitefly, aphid, thrips, mealybug, fungus gnat, weevil, leafhopper |
| Entomopathogenic fungus | Metarhizium anisopliae | Met 52®, Tick-EX, and others | Grasshopper, thrips, tick, spider mite, weevil, whitefly |
| Entomopathogenic fungus | Nomuraea rileyi | Nomuraea | Caterpillar |
| Entomopathogenic fungus | Verticillium lecanii | Mealikil® | Aphid, scale, whitefly |
| Entomopathogenic bacterium | Heat-killed Burkholderia spp. | Venerate® | Aphid, stink bug, leafhopper, small caterpillar |
| Entomopathogenic bacterium | Chromobacterium subtsugae | Grandevo® | Aphid, armyworm, cutworm, sod webworm, chinch bug, masked chafer, and oriental beetle, whitefly, thrips |
| Entomopathogenic bacterium | Bacillus papillae | Milky spore | Japanese beetle grub |
| Entomopathogenic bacterium | Bacillus sphaericus | Mosquito dunks and others | Mosquito larva |
| Entomopathogenic bacterium | Bacillus thuringiensis subspecies aizawai (Bta) | Agree®, XenTari® and other | Caterpillar |
| Entomopathogenic bacterium | Bacillus thuringiensis subspecies galleriae (Btg) | grubGone!® G and others | White grub |
| Entomopathogenic bacterium | Bacillus thuringiensis subspecies kurstaki (Btk) | Dipel®, Thuricide®, and others | Caterpillar |
| Entomopathogenic bacterium | Bacillus thuringiensis subspecies israelensis (Bti) | Gnatrol® and other | Larva of mosquito, blackfly, and fungus gnat |
| Entomopathogenic bacterium | Bacillus thuringiensis subspecies tenebrionis (Btt) | Novodor®, Trident®, and other | Colorado potato beetle, leaf beetle |
| Entomopathogenic protozoa | Nosema locustae | NOLO BAIT™ and others | Grasshopper |
| Entomopathogenic virus | Nucleopolyhedrosis virus (NPV) | NPV | Caterpillar |
Table 2. Commercially available biological control agents for plant pathogens.7
| Types | Species | Commonly known as | Target diseases |
| Bacterium | Agrobacterium radiobacter | Agrobacterium | Crown gall |
| Bacterium | Bacillus amyloliquefaciens | Double Nickel®, Stargus™ (strain F727), Taegro® 2 (strain FZB24) | Cercospora, Collectrichum, Phytophthora, Powdery mildew, Rhizoctonia, Sclerotinia |
| Bacterium | Bacillus licheniformis | Roots EcoGuard® and others | Dollar spot, anthracnose, brown rot (peaches) |
| Bacterium | Bacillus pumilus | Sonata® and others | Rust, downy mildew, powdery mildew, white mold, fire blight, scab, early and late blight, bacterial spot, northern and southern leaf blight |
| Bacterium | Bacillus subtilis | Rhapsody® (QST 713 strain), Companion® (GB03 strain), and others | Pythium, Fusarium, Phytophthora, Rhizoctonia, powdery mildew, Colletotrichum, Erwinia, Pseudomonas, Xanthomonas, Cercospora |
| Bacterium | Pseudomonas chlororaphis strain AFS009 | Zio™ and others | Colletotrichum. Rhizoctonia, Sclerotinia, Botrytis, Fusarium, Pythium, Phytophthora |
| Bacterium | Pseudomonas fluorescens | Pseudomonas fluorescens | Fireblight |
| Bacterium | Streptomyces spp. | Actinovate® and others | Fusarium, damping off, Pythium, Phytophthora, fire blight, Verticillium, Sclerotinia, downy mildew, Botrytis, powdery mildew, Botrytis, Phytomatotricum, Sclerotinia, Alternaria |
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