Biological pest control uses living organisms to suppress pest populations, and the examples span a wide range of creatures: predatory beetles that devour scale insects, tiny wasps that parasitize whiteflies, bacteria that destroy caterpillar guts, fungi that colonize aphids from the inside, and microscopic worms that hunt grubs underground. These natural enemies fall into three main categories, each with distinct mechanisms and real-world applications in agriculture, greenhouses, and home gardens.
Predators That Feed Directly on Pests
Predatory insects and other arthropods kill pests by consuming them outright, often eating dozens or hundreds of prey over their lifetimes. The most commonly used predators in biological control include lady beetles, ground beetles, rove beetles, lacewings, hover flies, predatory mites, and spiders. What makes arthropod predators especially useful is their relatively short life cycles. Their populations can rise and fall in step with pest numbers, creating a natural feedback loop that keeps damage in check.
The most famous success story in biological control involves a predatory lady beetle called the vedalia beetle. In the late 1800s, cottony cushion scale, an Australian insect that attacks over 200 plant species, devastated the California citrus industry. The vedalia beetle was imported from Australia and released into orchards, where it brought the scale under control so effectively that the program became the textbook example of classical biological control. The beetle works because it is a specialist predator with an extremely narrow prey range, feeding almost exclusively on cottony cushion scale and its close relatives. That same beetle has since been deployed in the Galápagos Islands, where cottony cushion scale appeared in 1982 and threatened native vegetation.
Parasitoids That Develop Inside Pest Insects
Parasitoids are insects, almost always wasps or flies, whose larvae develop on or inside a single host insect and eventually kill it. The adults live freely and often feed on nectar, pollen, or honeydew. Because parasitoids must be closely adapted to their host’s biology, defenses, and life cycle, they tend to attack a narrow range of species. That specificity makes them powerful biological control agents with minimal effects on non-target organisms.
One widely used parasitoid is a tiny wasp called Encarsia formosa, deployed worldwide in commercial greenhouses to control whiteflies on tomatoes, cucumbers, eggplant, poinsettias, and strawberries. Each female matures eight to ten eggs per day and lays them inside whitefly nymphs. The wasp larva develops inside the host, killing it. But the wasp also kills whiteflies a second way: it pierces nymphs with its ovipositor, feeds on the hemolymph (insect blood) for nutrition, and discards the host without laying an egg. This “host feeding” behavior means a single wasp destroys more pests than its egg-laying rate alone would suggest.
Growers release Encarsia formosa using several strategies. In longer cropping seasons, a small initial release can establish a self-sustaining parasitoid population that reproduces alongside the pest, a technique called inoculative release. In shorter seasons or on less favorable crops, repeated releases throughout the growing period keep parasitoid numbers high enough to maintain control.
Other parasitoid examples include wasps introduced against the Mexican bean beetle, the Colorado potato beetle, and the alfalfa weevil, all cases where a specialist parasitoid was matched to a specific agricultural pest.
Bacterial Agents: Bacillus thuringiensis
The best-known biological insecticide is based on a soil bacterium called Bacillus thuringiensis, commonly referred to as Bt. When insect larvae eat Bt spores, the toxin proteins activate in the insect’s highly alkaline gut (pH 9 to 10.5). The activated toxin breaks down the gut lining, and the larva dies of infection and starvation within one to five days. Young larvae are most vulnerable.
Different strains of Bt target different pest groups. One strain controls immature mosquitoes, flies, and gnats. Two other strains target caterpillars of moths and butterflies, making them useful against crop pests like corn borers and cabbage loopers. Additional strains control beetle larvae. This selectivity is one of Bt’s key advantages: because the toxin requires a specific gut chemistry to activate, it poses minimal risk to mammals, birds, and most beneficial insects. Bt products are sold as sprays and dusts for use on farms, in forests, and in backyard gardens.
Fungal Agents: Beauveria bassiana
While Bt works from the inside after being eaten, the fungus Beauveria bassiana attacks from the outside. It is a contact-based bioinsecticide, meaning the pest only needs to touch the fungal spores. Once spores land on an insect’s outer shell, they germinate and produce enzymes that break through the cuticle. The fungus then enters the insect’s bloodstream, rapidly colonizing the body from within and using the host’s tissues for nutrients.
Beauveria bassiana has an exceptionally broad host range, infecting over 700 insect species across most major insect orders. It kills both larvae and adults, targeting aphids, thrips, whiteflies, stink bugs, beetles, caterpillars, and chinch bugs. Commercial formulations are available as liquid suspensions and powders, registered for use on a wide range of agricultural and horticultural crops in the United States. Another fungal success story involves a pathogen of the gypsy moth that established a permanent, self-sustaining population after introduction and continues to suppress that pest without further human intervention.
Beneficial Nematodes in Soil
Entomopathogenic nematodes are microscopic roundworms that hunt insect larvae in soil. Two main groups are used in pest management, and they employ strikingly different hunting strategies. “Ambusher” species conserve energy by waiting near the soil surface and attacking mobile insects that pass by. “Cruiser” species actively move through the soil, following carbon dioxide, vibrations, and chemical cues to locate less mobile prey like white grubs (scarab beetle larvae) deep underground.
Once a nematode finds a host, it enters through natural openings like the mouth, breathing pores, or anus, and sometimes penetrates directly through thin spots in the insect’s outer shell. Inside the body cavity, the nematode releases symbiotic bacteria from its gut. These bacteria multiply rapidly in the insect’s bloodstream, and the host typically dies within 24 to 48 hours. After the host dies, the nematodes feed on the decaying tissue, mature, reproduce, and release a new generation of juveniles into the soil to find fresh hosts. Beneficial nematodes are commercially available and applied by mixing them into water and spraying or drenching the soil, making them practical for lawns, gardens, and commercial turf.
Three Approaches to Using Natural Enemies
Not all biological control involves buying and releasing organisms. There are three distinct strategies, and understanding them helps explain why some programs are one-time efforts while others require ongoing management.
Classical biological control involves importing a natural enemy from another region, usually the pest’s native range, and releasing it to establish a permanent population. The vedalia beetle program is the classic example. In the United States, candidates for classical biocontrol undergo rigorous quarantine testing to confirm they won’t attack native, non-target species before they’re approved for release. When it works, the natural enemy reproduces on its own indefinitely, and no further releases are needed.
Augmentative biological control means mass-producing natural enemies and releasing them into crops, either as a one-time inoculation early in the season or as repeated “flooding” releases throughout the growing period. Greenhouse releases of Encarsia formosa wasps and soil applications of beneficial nematodes are typical augmentative approaches. The organisms may or may not establish lasting populations; the goal is immediate pest suppression during the current crop cycle.
Conservation biological control focuses on modifying the environment to support natural enemies already present in the landscape. Practical techniques include planting insectary strips of flowering plants within or around crop fields to provide nectar, pollen, and shelter for beneficial insects. Beetle banks, which are low berms of dense grasses placed within fields or along fence rows, give ground beetles and other predators habitat to overwinter and hunt from. Cover crops, careful mowing schedules, alternate-row harvesting, and windbreak plantings that reduce dusty conditions (which favor pest mites and inhibit predatory mites) all fall under this strategy.
A Growing Global Market
The biopesticides market, which includes biological control organisms and naturally derived pest control products, was valued at $7.72 billion in 2024 and is projected to nearly double to $17.68 billion by 2030, growing at about 14.6% per year. North America accounts for the largest share at roughly 40% of global revenue. The fastest-growing segment is bionematicides, products targeting pest nematodes, reflecting increasing demand for soil-health-focused pest management. These numbers signal a broad shift in agriculture toward integrating biological tools alongside, or in place of, conventional chemical pesticides.