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Biocontrol in Action – Nematodes As Natural Pest Predators

Biological control involves using living organisms (predators, parasitoids, or pathogens) to manage pest populations. It is most effective in light sandy soils and when applied several times throughout the growing season.

Entomopathogenic nematodes Steinernema feltiae and S. carpocapsae are standard products sold for leatherjacket control. A product containing the predatory wasp Heterorhabditis bacteriophora is also available.


Predatory nematodes are microscopic, worm-like creatures that feed on other soil-dwelling organisms such as insects. These natural pest predators have become increasingly popular as a way to control pests without chemical pesticides.

These nematodes hunt or ambush their prey, then pierce the insect through its natural openings (anus, spiracles, mouth) and release bacteria that cause disease and ultimately kill it. They are effective against various pests, including mushroom flies, thrips, fungus gnats, and tipulids.

Some nematode species, such as Steinernema feltiae and Heterorhabditis carpocapsae, are often purchased in commercial products to control specific pests. These are typically released in the late summer or early autumn as the infective third-stage juveniles.

Other nematode species that can be used as biological controls are more difficult to mass-produce (e.g., entomopathogenic nematodes in the genera Heterorhabditis and Steinernema) because they have narrow host specificities against minor pests or modest virulence. Research into improving the effectiveness of these nematodes could involve the selection and induction of variants that are more virulent or have other desirable characteristics.


Biological control is the intentional manipulation of natural enemies to supplement pest control. Parasites are a significant group of organisms used in biocontrol. They may be generalists, consuming a range of different host species, or specialists, attacking only a limited number of closely related species. Some parasites gain entry into hosts by fecal-oral penetration (e.g., helminths, Giardia, Cryptosporidium, and some protozoans), direct penetration through the skin (e.g., malaria), or through a vector’s bite (e.g., leishmaniasis).

Most highly specialized parasites attack only a few closely related pest species. Biological control involves finding a pest’s native complement of parasites, predators, and pathogens and then introducing these into an area where the pest is established. This is a complicated process, requiring extensive research into the pest’s biology and the ecology of its natural enemies and careful consideration of the risk of unintended consequences in the target ecosystem. Major predaceous organisms include birds, fish, amphibians, reptiles and mammals, ants, beetles, dragonflies, damselflies, flies, thrips, true bugs, lacewings and their relatives, beetle larvae and adults, spiders and mites.


Predators include animals that kill and eat pest species and those that capture or parasitize them. Major predators in fruit production systems include birds, amphibians and reptiles, mammals, and arthropods such as ground beetles (lady beetles, rove beetles, true bugs, mantids, flower bugs, thrips, flies, and hover flies), spiders, and mites.

Parasites can be bacteria, fungi, or viruses that kill, infect, or debilitate their host plants. Some pathogens attack seedlings or other young, tender parts of a plant, while others attack mature tissues.

Classical biological control involves finding a natural enemy in the pest’s native habitat and importing it to the new area, where it is released and hopes that it will establish itself and become permanent. This is sometimes referred to as “inundative release.” It has often been used for introduced or “exotic” pests, whose populations have become unusually abundant and overrun their indigenous natural enemies. Invasive weeds and some insects are also controlled this way.


Biological control relies on the natural behavior of living organisms to suppress pest populations and make them less damaging. This is called classical biological control. Researchers discover what kinds of organisms naturally attack a pest in this process. Then, they search for and collect these organisms in their native habitat. They study them carefully to ensure they are safe and suitable for release. They are then shipped back to the pest’s location and released.

The nematodes Steinernema feltiae and Heterodera schachtii can be used to kill caterpillars, thrips, wireworms, oriental fruit moth larvae, and other lepidopterous insects in top fruits such as apples and peaches, vegetables like potatoes and tomatoes, and outdoor crops such as onions and beans. They can be tank-mixed with most chemical herbicides, fungicides, and insecticides. Still, they should not be applied with broad-spectrum chemicals that persist long in the soil, such as carbaryl* (Benol) or organophosphates such as malathion.

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