FEATURE ARTICLE

The General Approaches To Insect Control: An Overview

Biological control is one of several general approaches to insect pest management. When developing an overall pest management strategy it is helpful to consider all of the available options. Most specific insect control methods can be classified into the following major categories: cultural control, host resistance, physical control, mechanical control, biological control, and chemical control.

CULTURAL CONTROLS involve modification of standard farm practices to avoid pests or to make the environment less favorable for them. There are several types of cultural controls; the following are a few examples of commonly used methods. Crop rotation replaces a crop that is susceptible to a serious pest with another crop that is not susceptible, on a rotating basis. For example, corn rootworm larvae can be starved out by following corn with one to two years of a non-host crop such as soybeans, alfalfa, or oats. Sanitation refers to keeping the area clean of plants or materials that may harbor pests. Examples include removal of weeds in greenhouses that may harbor mites, aphids, or whiteflies; destruction of crop residues such as corn stubble, squash vines, or fallen apples that may be overwintering sites for pests; cleaning of farm equipment that can spread pests from field to field; and removal and management of manure that provides breeding sites for flies. The planting of several crops in close proximity is called polyculture (as opposed to monoculture), a practice that makes it difficult for pests to find their favored host crop and also promotes favorable habitat for beneficial natural enemies. Many field crops, such as alfalfa, soybeans, corn, and small grains can be planted in parallel strips, a practice called strip cropping, which again creates the habitat diversity favorable to natural control. Trap cropping is the provision of a pest insect's preferred food near the crop to be protected; the insects are attracted to the trap crop which is then destroyed. For example, pickleworms will concentrate in squash planted near cucumbers, and the squash plants can be destroyed. A carefully considered time of planting will help avoid some pest problems such as seed corn maggot.

HOST RESISTANCE, or plant resistance, has been used effectively for decades to reduce the impact of pests. Some plants have physical and chemical adaptations that allow them to repel, tolerate, or even kill pests. Plant breeders attempt to use these characteristics and even improve them to develop crops that are resistant. Many varieties of important crops grown today, such as wheat, rice, alfalfa, corn, and apples are resistant to one or more pests. Historically, the development of resistant varieties was often tedious and lengthy, requiring many generations of plant hybridization. Although such traditional techniques will continue, it is likely that modern methods of biotechnology will also provide pest-resistant crops.

PHYSICAL CONTROLS are methods that physically keep insect pests from reaching their hosts. Barriers include window screens for keeping health and nuisance pests out of buildings and plant pests out of greenhouses, floating row covers for many horticultural crops, and plant collars to keep cutworms from attacking plants such as tomatoes. Various types of traps can be used for control, such as cockroach traps in homes. Codling moth larvae can be trapped under cardboard bands wrapped around apple trees; the bands are removed and destroyed.

MECHANICAL CONTROLS directly remove or kill pests. Mechanical control methods can be rapid and effective, but many are mostly suited for small acute pest problems, and are popular with gardeners and homeowners. Importantly, mechanical controls have relatively little impact on natural enemies and other non-target organisms, and are therefore well suited for use with biological control in an integrated pest management approach (see below). Cultivation or tillage exposes many soil insects to desiccation or predation by birds. Hand-picking can be used for large or brightly colored foliage feeders such as Colorado potato beetle, Mexican bean beetle, and tomato hornworm. Shaking plants will dislodge many pests. For example, plum curculio beetles can can be removed from fruit trees by diligently banging tree limbs with a padded stick and collecting the adult weevils on a white sheet as they fall out of the trees. A strong spray of water will dislodge aphids and mites from greenhouse, garden, and house plants. Fly swatters and mouse traps are forms of mechanical control.

BIOLOGICAL CONTROL, the use of beneficial organisms to control pests, is the subject of this newsletter; it is included here to identify it as one of the major general approaches to pest management. Microbial control is a form of biological control that uses insect pathogens, such as viruses, bacteria, and fungi, to control pests. Microbial control will be a frequent subject in this newsletter.

CHEMICAL CONTROL is the use of chemicals to kill pests or to inhibit their feeding, mating, or other essential behaviors. The chemicals used in chemical control can be natural products, synthesized mimics of natural products, or completely synthetic materials.

Repellants, confusants, and irritants are not usually toxic to insects, but interfere with their normal behavior and thereby keep the insects from causing damage. Mothballs and mosquito repellants are familiar examples. Widescale use of synthetic sex pheromones may confuse insects sufficiently that they are unable to mate and produce offspring; a few such products are commercially available, such as for codling moth control in apples. Using insect pheromones in this manner is called mating disruption, a practice that works best in large commercial plantings where it is less likely that mated females will move into the planting from outside of the treated area. Many of these types of behavioral chemicals break down or wash away quickly, and must be reapplied frequently, used in an enclosed area, or formulated to release slowly over a long period.

Insecticides and miticides include many types of commercially available toxins, some naturally-derived, others synthesized, that are used for killing insects and mites.

Chemical controls, particularly synthetic organic insecticides, have been developed for nearly every insect pest. They are widely used in industrialized nations for several reasons: they are highly effective -- one product often controls several different pests; there is relatively low cost for product or labor; and generally their effects are predictable and reliable. Chemical insecticides have allowed management of larger acreages by fewer individuals because of the reduced labor needed for physical and mechanical controls. Besides their use in agriculture, chemical insecticides have been very important in the battle against disease-carrying insects, such as mosquitoes that carry malaria.

However, chemical controls have many disadvantages: most have biological activity against many forms of life and therefore can affect non-target organisms; for the same reason, they present various levels of hazard to humans, especially pesticide applicators and other farm workers; most are highly toxic to beneficial insects, such as pollinators and predatory and parasitic natural enemies; both target and non-target insects can develop resistance to insecticides, sometimes very rapidly. Over-reliance on chemicals and diminished use of other control methods have helped push agriculture away from a more natural, balanced state.

INTEGRATED PEST MANAGEMENT (IPM) is the blending of all effective, economical, and environmentally sound pest control methods into a single but flexible approach to managing pests. Those who practice IPM realize that it is neither possible nor economically feasible to eliminate all pests; instead pest populations should be managed below economically damaging levels. Users of the IPM approach recognize and understand the importance of the controls provided by nature. When human intervention is necessary, the least invasive practices, such as plant resistance, biological control, and cultural control, should be used because these are the practices that fit best into sustainable agriculture. Highly disruptive or environmentally damaging practices should be used only as a last resort. Chemical pesticides should be used only when necessary, based upon frequent and routine monitoring of pest populations. Natural enemy populations should also be monitored so that their impact on pests can be determined. When pesticides are necessary, if possible, only those products should be used that are not detrimental to natural enemies.

Integrated pest management is a dynamic and evolving practice. Specific management strategies will vary from crop to crop, location to location, and year to year, based upon changes in pest populations and their natural controls. As specific new approaches are developed, these too can be incorporated into the program as appropriate. Modern pest managers will be most effective if they are knowledgeable about their pests, beneficials, and all of the control options available.

Adapted from


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