Strategies to Reduce Insect Populations | Invertebrates | Zoology

Insect pest management is defined as the use of management strategies to reduce (or maintain) insect populations to levels that do not cause economic injury. One goal of insect pest management is to use control strategies that result in the suppression of the target organism(s) without disruption to non-target organism(s). Control strategies are commonly categorized into biological control (biocontrol), chemical control, cultural control, regulatory control, and mechanical/physical control.

Biological Control to Reduce Insects:

Biological control is the action of natural enemies (e.g., some phytophagous species that are weed feeders, parasitoids, and predators) that result in the death or suppression of pests. Some authorities recognize pathogens and naturally occurring plant and animal products that control insects as bio control agents [e.g., pheromones, plant and animal odors (baits), and pathogens].

A parasitoid is a specialized organism that is usually about the size of its host as an adult; the immature stage kills its host internally or externally and requires only one host for development into the free-living stage (adult).

A predator is an organism that is usually larger than its prey, kills its prey by feeding externally, requires more than one prey to complete its development, and is a free-living organism throughout its life. A pathogen is a microorganism, including viruses, that causes disease. Biological control can be naturally occurring, classical, or augmentative. Each method requires a different amount of manipulation.

Naturally occurring bio control is not actively manipulated. It is the background mortality due to naturally occurring organisms in the plant or animal system. Classical bio control and augmentative bio control refer to active use and management of natural enemies by humans.

In classical bio control, the natural enemy is released in the range of the pest insect over a relatively short period of time (possible only one release or as much as several releases per year for several years).

Afterward, recovery efforts may be made to determine the rate of success of the natural enemy, but regular long-term releases are not made. Initial manipulative efforts may be large, but this is a very low- input sustainable pest management system if the bio control agent is successful in reproducing, overwintering, and controlling the pest.

Even partial control of the pest is beneficial because such control often helps other control efforts. Augmentative bio control differs from classical bio control in that regular long-term releases are scheduled. Much more manipulation is required in augmentative bio control efforts.

Therefore, such efforts are usually restricted to systems in which the bio control agent does not permanently establish in the release area, but the crop or animal value and pest status is sufficient to warrant the cost in continually releasing the bio control agent.

Is biological control feasible? Obviously, naturally occurring bio control is always advantageous because it requires no artificial inputs. Assistance can be provided to naturally occurring bio control by using insecticides that are less harmful to bio control agents, and by scheduling insecticide use only when necessary to control pests that are expected to cause economic damage.

Overall advantages in using bio control:

a. Often specific to the target pest.

b. Off-target effects are minimal.

c. Often very cost efficient (particularly in the case of naturally occurring and classical bio control).

d. There is a cumulative long-term control effect, with naturally occurring and classical bio control, because the natural enemy persists Overall disadvantages in using bio control.

Some of these disadvantages are as follows:

a. Impact on the pest species is often slows (often a gradual reduction in pest population over multiple generations).

b. Not compatible with most insecticides (most broad spectrum insecticides will kill the pest species and its natural enemies).

c. Conditions (such as climate) may prevent use of classical bio control or hamper the ability of naturally occurring bio control to reduce pest populations below a level of economic concern. In such cases augmentative bio control is a bio control option, but it can be excessively expensive.

d. Cannot be regarded as a second line of defense to be used if other methods fail because the control strategy is slow- acting.

Chemical Control to Reduce Insects:

Chemical control is the use of chemical compounds to kill and/or reduce numbers of insects. There are diverse opinions about what constitutes an insecticide. Broadly defined, an insecticide is a chemical (synthetic or naturally occurring) with toxic (causes death or illness), inhibitory (such as repellents), or protective action against insects.

This definition identifies as insecticides synthetic broad and narrow- spectrum compounds and naturally occurring plant and animal compounds with insecticidal activity. Narrowly defined, an insecticide is a synthetic chemical with toxic, inhibitory, or preventive action. This definition includes synthetic broad- and narrow-spectrum compounds and man-made mimics of naturally occurring plant and animal compounds with insecticidal activity.

Insecticides are regulated by federal and state agencies. These agencies determine the classification of an insect “chemical” control agent. As detection of compounds with narrow spectrums of biological activity increases, the distinction between chemical control and biological control may become less clear.

Biological control identifies naturally occurring plant and animal products for insect control as bio control agents. But by one definition of chemical control, the same chemical product synthetically produced would be classified as an insecticide. It may be best to consider the spectrum of activity of the control agent.

A “good” chemical or biological control agent should restrict killing activity (whether it is due to toxic action, predation, or parasitism) to the target organism(s) with no adverse activity on non- target organisms, including natural enemies and humans. Unfortunately, more than 95 percent of insecticide use involves broad- spectrum products that have limited compatibility with biological controls. Some newer products and others in development have narrower spectrums of activity.

Overall advantages in using chemical control:

1. Impact on the pest species is often quick.

2. There is often limited cumulative long-term control effects (limited persistence in the environment).

3. Often compatible with other chemical compounds (e.g., herbicides).

4. Can be used as a second line of defense if other methods fail because of their quick action.

Overall disadvantages in using chemical control:

1. Because there is often limited cumulative long-term control effects, products must often be reapplied.

2. Persistence may be a problem with some products (detrimental persistent effects such as groundwater contamination and toxic effects due to bioaccumulation).

3. Often a lack of target specificity (e.g., off-target effects are often great).

4. Applicator safety must be carefully considered because of off- target effects, including mammalian effects.

Some characteristics are listed as advantages and disadvantages. The nature of the specific chemical in consideration will determine if, for example, long residual activity is an advantage because of extended insect control or a disadvantage because of environmental contamination.

Cultural Control of Insects:

Cultural control is the reduction of insect populations or their effects through agricultural practices. Cultural control involves change of normal fanning practices rather than addition of special procedures. The best cultural controls become stable fanning practices (often serving multiple purposes), and it is often forgotten that insect control was one reason for establishing the practice.

Examples of cultural control include:

1. Plant resistance to insect attack (host plant resistance).

2. Crop rotation (rotating out of a susceptible crop into a crop that is tolerant of an established insect pest population).

3. Crop residue destruction and sanitation to reduce an insect pest population.

4. Timing of planting to avoid insect damage.

Regulatory Control to Reduce Insects:

Regulatory control is the regulation of an area to eradicate, prevent, or manage insects and their injury to plants, animals, and humans. Agencies involved in regulatory control are the USDA Animal and Plant Health Inspection Service, the US Post Office, state departments of agriculture, and weed and pest control districts.

Examples of regulatory control include:

1. Quarantine:

Regulations forbidding sale or shipment of plants, plant parts, or animals, usually to prevent spread of diseases, insects, nematodes, or weeds.

2. Host-Free Periods:

Periods of time in which the host plant is not planted, allows for possible disruption of the insect life cycle.

3. Eradication:

Complete destruction of a pest from a region.

Mechanical and Physical Control to Reduce Insects:

Mechanical and physical controls use machines, implements, or climatic conditions for the control of insects (often part of cultural control).

Examples of mechanical or physical controls include:

1. Flow down cultivation to disrupt insect activity.

2. Use of screens and traps to limit activity of insects or directly kill them.

3. Hot/cold storage or treatment to directly kill an infestation or make the environment unattractive for insect colonization.

The greatest challenge in insect management is the selection of the most appropriate combination of control strategies. Farmers and ranchers are challenged to provide consumers with wholesome, safe food and minimize adverse impacts on the environment. While earning an adequate profit, a combination of compatible management strategies should be used if available, to produce a more stable insect management system.

Remember, an appropriate goal of insect pest management is to use control strategies that result in the suppression of the target organism(s) without disruption to non-target organisms.

Insecticide use may be warranted, but should be implemented only if the cost of control (insecticide and application costs) is lower than the anticipated loss if an insecticide is not used.

Such decisions must be based on the understanding of yield and insect damage potential, market crop value, cost of Managing the insect, and effectiveness of the insecticide. Also, consideration should be given to the non-target effects of the insecticide such as natural enemy kill and environmental effects.

For a few insects and agricultural production systems, effort has been made to combine these factors into an insect density threshold, called the economic threshold, at which point a farmer should implement a chemical control. If an economic threshold is available for an insect/plant or insect/animal system, it should be used to better ensure use of insecticides only when needed.

Through this approach, the fanner can strive for an agricultural production system that increases the inherent productive capacity of the land to allow for adequate profit, to provide consumers with wholesome, safe food, and to minimize adverse impacts on the environment.