9.19 Insect Control

Are ladybugs dangerous?

Ladybugs won't hurt you. But they are dangerous to some other insects! This ladybug is eating plant-harming bugs known as aphids. Since they have an appetite for aphids, ladybugs are a farmer's friend.

Control of Insects

Though insects can be very important, some are also considered pests. Common insect pests include:

1. Parasitic insects, such as mosquitoes, lice, and bed bugs.
2. Insects that transmit diseases, including mosquitoes and flies.
3. Insects that damage structures, such as termites (Figure below).
4. Insects that destroy crops, including locusts and weevils.

Termites can destroy wooden structures.

Many scientists who study insects are involved in various forms of pest control. Most utilize insect-killing chemicals, but more and more rely on other methods. Ways to control insect pests are described below.

Biological Control

Biological control of pests in farming is a method of controlling pests by using other insects (or other natural predators of the pests). Biological control of insects relies on predation and parasitism. Insect predators, such as ladybugs and lacewings, consume a large number of other insects during their lifetime. If you add ladybugs to your farm or garden, they will help keep insect pests, such as aphids, under control. Aphids are among the most destructive insect pests on cultivated plants in temperate regions, so any control of these pests is beneficial.

Ladybugs also consume mites, scale insects and small caterpillars. The larvae of many hoverfly species also feed upon aphids, with one larva consuming up to fifty aphids a day, which is about 1,000 in its lifetime. They also eat fruit tree spider mites and small caterpillars. Dragonflies are important predators of mosquitoes, and can be used to control this pest. Parasitic insects include insects such as wasps and flies that lay their eggs on or in the body of an insect host, which is then used as a food for developing larvae. The host is ultimately killed. Caterpillars also tend to be one likely target of parasitic wasps.

Chemical Control

Chemical control of pests involves the use of insecticides. Insecticides, which are also known as pesticides, are most often used to kill insects. Insecticides are chemicals that kill insects. The U.S. spends $9 billion each year on pesticides. Disadvantages to using pesticides include human, fish, and honeybee poisonings, and the contamination of meat and dairy products.

When choosing to use an insecticide, there are numerous points to consider. Negative effects of the pesticide should try to be minimized. Important questions to consider include the following.

• What is the chemical's success against the target pest? Will the insecticide provide the desired level of control of the pest? If the answer is no, other methods of control should be considered.

• Does the chemical have an impact on natural enemies of the pest? In large scale efforts to rid areas of mosquitoes, the insecticide used also killed the dragonfly. This effort removed a natural predator of the mosquito. This may be an unacceptable negative effect of using the insecticide.

• How susceptible is the crop to insect damage? If the crop is not heavily damaged, only minor pest control may be needed. This may affect the amount or type of insecticide used.

• How toxic is the chemical to the environment and humans? Some older insecticides are extremely poisonous. Keep in mind that users of these poisons have a community responsibility to minimize the contamination of the surrounding environment, as well as keeping animals, surrounding crops and humans safe.

• Does using the pesticide result in the development of resistance? If so, this can make additional use of the pesticide less effective. As the resistance will be passed to future generations of the insect (which is natural selection in action), this could be considered a negative side-effect of pesticide use.

Summary

• Harmful insects include those that can destroy buildings and crops or transmit disease.
• Insecticides are commonly used to control insect pests, but they can have harmful effects on the environment.

Explore More

Use the resources below to answer the questions that follow.

Explore More I

• Deadly Mating at http://www.youtube.com/watch?v=m2H-uTg51_c (3:05)

1. How are farmers seeking to control diamondback moths (Plutella xylostella)?

Explore More II

1. What is an entomologist?
2. What is a danger of introducing a new insect as a biological control mechanism?
3. Why do people like biological control for food crops?

Review

1. What are three examples of insects that are pests?
2. Name two ways that insects can be pests.
3. What is meant by biological control of insects?
4. What are two disadvantages to pesticides?