Biological Control of Pests

By the 1950s, the use of synthetic insecticides to defend food and fiber crops against insects, mites, and disease appeared to offer an easy solution to crop protection. More than 50 years later, while conventional agricultural methods still rely mainly on the use of chemical pesticides, we recognize that there are many problems associated with the use of insecticides, such as the following:

• Some insect pests become resistant
• Nontarget organisms can be affected
• Pest resurgence can occur
• Adverse affects on environment and human health can arise

In response to the consequences of petrochemical pesticide use, researchers and agriculturalists have developed the Integrated Pest Management (IPM) system, an eco-based pest-control strategy that strives to minimize the use of chemical pesticides by embracing such practices as the use of pest-resistant plants, various cultural control methods, and biological control—the use of pests’ natural enemies to suppress their populations and minimize their damage to crops. All insect pests have natural enemies, and they are classified as follows:

• Parasitoids: species whose immature stage develops on or within a single insect host, ultimately killing the host; many species of wasps and some flies are parasitoids
• Predators: free-living species, such as lady bugs, with prodigious appetites for prey
• Pathogens: disease-causing organisms including bacteria, fungi, and viruses; they kill or debilitate their host and are relatively specific to certain insect groups

When choosing a natural enemy to combat a pest, there are several characteristics to look for in the natural enemy, such as a high reproductive rate, good searching ability, host specificity, adaptability to different environmental conditions, and the capacity to be [Page 55]synchronized with its host. Because it requires a deep understanding of the pests and their natural enemies as well as of the crops and environment—and of the interrelationships that exist between all of these components—biological control of pests usually involves an active human role. The goal of the biological control of pests is not to completely eliminate all pests, but to reduce their numbers, and thus, the damage they cause.

Biological control of pests involves three broad, overlapping methods:

• Conservation
• Classical biological control
• Augmentation

The conservation of natural enemies is probably the most important and readily available biological control method available to growers. Natural enemies occur in all agricultural systems, and they are adapted to the local environment and to the target pest, and their conservation is generally simple and cost effective. Classical biological control is the practice of importing, and releasing for establishment, natural enemies to control pests. While it typically involves traveling to the area from which a newly introduced, or “exotic,” pest originated, and returning with some of its natural enemies, it is sometimes used on native insect pests. New pests are constantly arriving accidentally or intentionally, and they often survive; when they do, it is usually because their enemies were left behind. Introducing some of their natural enemies can be an important way to reduce the amount of harm exotic pests can do. After procuring the natural enemies, they are subjected to a meticulous quarantine process to ensure that no unwanted organisms, such as hyperparasitoids, are present; the natural enemy is then reared, ideally in large numbers, and released. Follow-up studies are conducted to determine if the natural enemy is successfully combating the pest and to assess the long-term benefit of its presence.

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