Chapter 12

Insect Pest Management for Organic Crops

Biological Control of Insect Pests

Biological control uses natural enemies—usually called “beneficial insects” or “beneficials”—to manage pests. Natural enemies include insect predators (insects that consume part or all of pest insects), parasitoids (insects that use other insects to produce their offspring, thereby killing the pest insect in the process), and pathogens, including viruses, bacteria, protozoa, fungi, and nematodes (diseases that kill or decrease the growth rate of insect pests). The goal of biological control is to hold a target pest below economically damaging levels—not to eliminate it completely—since decimating the population also removes a critical food resource for the natural enemies that depend on it. Biological control is often most effective when coupled with other pest control tactics in an integrated pest management (IPM) program. Practices that are often compatible with biological control include cultural controls, crop rotation, insectary plantings, trap crops, planting pest-resistant varieties, using approved insecticides with selective modes of action, or spot treatments that leave untreated areas to serve as refuges for natural enemies.

Types of Natural Enemies for Biological Control

Predators, parasites, and pathogens are the primary groups used in biological control of insects and mites. Most parasites and pathogens, and many predators, are highly specialized and attack a limited number of closely related pest species.

Predators

Predators include birds, fish, amphibians, reptiles, small mammals, and arthropods. Arthropods (insects, mites and spiders) are the most important predators in pest management and include lady beetles, ground beetles, syrphid flies, green lacewings, assassin bugs, predaceous bugs, minute pirate bugs, predatory mites, and spiders (See Table 12.2). Predators are usually larger than the prey, which they capture and kill.

Parasitoids

Parasitoids are often called parasites, but the term parasitoid is more technically correct. Most beneficial insect parasitoids are wasps or flies, although other insects may have life stages that are parasitoids as well (See Table 12.2). By definition, insect parasitoids have a free-living adult stage and an immature life stage that develops on or within an insect host and ultimately kills it.

Pathogens

Natural enemy pathogens are microorganisms including certain bacteria, fungi, viruses, and nematodes that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. Some pathogens have been mass produced and are available in commercial formulations for use in standard spray equipment.

General Approaches to Biological Control

Effective biological control often requires a good understanding of the biology of the pest and its natural enemies, as well as the ability to identify various life stages of relevant insects in the field. There are three broad approaches to the biological control of insects: 1) augmentation of existing natural enemies by releasing predators or parasites; 2) conservation of natural enemies by changing aspects of the environment that threaten their survival or effectiveness; and 3) importation of natural enemies.

Augmentation of Natural Enemies

Augmentation is an attempt to reduce a pest’s population to noneconomic levels by temporarily increasing natural enemy numbers in an area through periodic releases. The natural enemies then seek out and attack the insect pest. Increasing the natural enemy population improves the chance of gaining economic control over the pests. Natural enemy augmentation is based on the assumption that, in some situations, there are not adequate numbers of natural enemies to provide sufficient biological control (even though some may be present), or that their immigration is not timely enough to suppress the pest before it reaches economic levels. Today, commercial natural enemies are available for controlling aphids, mites, scale insects, mealybugs, leafminers, thrips, caterpillars, and other insect pests.

Conservation of Natural Enemies

The second approach, conservation, involves boost populations of existing or naturally occurring beneficial organisms such as predators, parasitoids, and pathogens by supplying them with appropriate habitat and alternative food sources. “Farmscaping” is a term sometimes used to describe the creation of habitat to enhance the chances for survival and reproduction of beneficial organisms. It involves identifying the factor(s), which may limit the effectiveness of a particular natural enemy and modifying them to increase the effectiveness of the beneficial species.

Importation of Natural Enemies

Classical biological control differs from the other two general methods (augmentation and conservation) because it is not directly conducted by the grower. International agencies, federal agencies (especially U.S. Department of Agriculture, USDA), and state agencies (state departments of agriculture and land-grant universities) are responsible for identifying potential target pests, locating their natural distributions, searching these areas for candidate natural enemies, and introducing selected natural enemies into the necessary areas. Indeed, specific quarantine laws prohibit private individuals or agencies from introducing non-native organisms (including natural enemies) without proper authorization from USDA.

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