Biological Control of Insect and Weed Pests in North Dakota Agriculture

E-1225, January 2002

Laurence D. Charlet, USDA, ARS, Research Entomologist
Denise Olson, Assistant Professor
Phillip A. Glogoza, Extension Entomologist

Contents

Introduction
Biological Control
        - Parasites
        - Predators
        - Diseases
Maintaining Natural Order
        - Canola Insect Pests
        - Potato Insect Pests
        - Sunflower Insect Pests
        - Sugarbeet Insect Pests
        - Corn Insect Pests
       - Small Grain Insect Pests
Weeds
       - Leafy Spurge
       - Purple Loosestrife
Conclusions
Biological Control References

IPM is an ecologically-based pest management strategy that forms a part of the overall crop production system. Ideally, it incorporates all appropriate methods from many scientific disciplines into a systematic approach to minimize pest damage. IPM control tactics include a variety of approaches including cultural control, resistant plant varieties, chemical control, and biological control.

The use of biological control is a fundamental tactic for pest suppression within an effective Integrated Pest Management (IPM) program. Biological control refers to the use of natural enemies against a pest population to reduce the pest's density and damage to a level lower than would occur in their absence.

Biological control as a management tool dates back over 1,000 years when ancient Chinese citrus growers used ants to control caterpillar larvae infesting their trees. It is one of the safest methods of control since it is not toxic, pathogenic or injurious to humans.

Biological control has the advantage of being self-perpetuating once established and usually does not harm nontarget organisms found in the environment. In addition, it is not polluting or as disruptive to the environment as chemical pesticides, nor does it leave residues on food, a concern to many people today. However, the use of biological control does require detailed knowledge of the pest's biology and population dynamics, as well as the natural enemies associated with the pest and their impact. Control is usually not complete with this IPM method since a residual population of the pest is often necessary for the natural enemies to remain in the environment, so some noneconomic population levels of pests must be acceptable or tolerated.

Biological control also fits well in combination with other IPM strategies. There are many factors (crop, pest complex, environment) that can influence the success of beneficial organisms in reducing pest densities to manageable levels. In many situations the biological control method will need to be utilized in concert with other tactics. Selecting the least disruptive management tactic is recommended by IPM and should help conserve natural enemies.

The use of biological control to manage pests is divided into three types of approaches. Importation refers to the search for better natural enemies to introduce and permanently establish. The need for importation biological control occurs when a pest is accidentally introduced into an area and its natural enemies are left behind. An attempt is made to locate these enemies and introduce them to reestablish the control that often existed in the native range of the pest. This may be from another country or another region of the same country.

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 pest. In some cropping systems, technology has been developed to rear natural enemies artificially so these releases can be made economically. A number of commercial companies have been created to produce a wide variety of natural enemies, both predators and parasites.

The third approach, conservation, is concerned with protecting the natural enemies that are already present in an area. In conservation, an attempt is made to manipulate the environment or the farming practices to protect the natural enemies or provide needed resources (e.g. alternate prey or food for adults) for them to survive and build up populations to levels where they can manage the pest and prevent it from causing economic damage to crops. Naturally occurring or indigenous natural enemies prevent many plant-feeding insects from achieving pest status. Conservation of these natural enemies allows them to operate near their full potential. Conserving natural enemies requires the use of farming practices that are less disruptive to natural enemy populations. Insecticide use destroys the target pest as well as many natural enemies that are present. Reduced or carefully timed insecticide treatments lower the negative impact on beneficial organisms. Effective conservation of natural enemies depends on: understanding the agroecosystem; use of selective pesticides; use of the least disruptive formulation of the chemical; application of the insecticide only when necessary and based on reasonable economic injury levels of the pest; and pesticide application at the time or place that is the least injurious to natural enemies.

Natural enemies of insect pests fall basically into three types. Parasite (also called parasitoid) adults are free-living; the immature stage lives on or inside a host and kills the host before the host completes its development. Parasites lay one or more eggs on the outside of the host body or they insert the eggs inside their host. The immature parasite feeds on the host and requires only a single individual prey to complete its development. Free-living adults may feed on nectar from flowering plants or obtain nutrients by piercing the body of host insects and withdrawing fluids (host-feeding). Parasites attack a particular stage of the host, but all host stages are attacked by various parasites. Parasites are often small, easily overlooked and can be difficult to distinguish from other small nonparasitic flies and wasps. Parasites are not harmful to humans and tend to attack and parasitize one, or at most a few, closely related species of pest insects.

Parasites are usually members of the order Hymenoptera (wasps, Figure 1) and a few are members of the order Diptera (flies, Figure 2). Parasites are often considered more effective natural enemies than predators because many have a narrower host range, require only one host to complete development, have an excellent ability to locate and kill their host and can respond rapidly to increases in host populations. There are thousands of different species of parasites in North America. Most insects, including pest insects, are attacked by one or more species of parasites.

Figure 1. Parasitic wasp.  (Click here for a 26KB color photo of a parasitic wasp.)




Figure 2. Parasitic fly. (Click here for a 21KB color photo of a parasitic fly.) 

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E-1225, January 2002