The Unintended Side Effects of Introduced Predators

Sometimes introduced predators become a bigger problem than the pests they were introduced to control. For example, barn owls were introduced in Mauritius in the 1940s and 1950s to control rats. They certainly ate the rats, but also preyed upon native species of birds, such as fairy terns, and there is now a reward for killing barn owls. The small Indian mongoose was introduced to a number of Caribbean islands in the nineteenth century to kill the rats and snakes that infested sugarcane fields. Again, the mongooses did kill the rats and snakes, but their populations grew and they began to also kill a number on species of native birds, reptiles, and mammals. In Jamaica, the mongoose has been linked to the extinction of five native species—one lizard, one snake, two birds, and one rodent.

from India to help control locusts. Charles Valentine Riley (1843-95) is said to be the father of modern biological pest control. In 1873, he shipped an American predatory mite to France to protect against an insect that was destroying grapevines. His actions helped save the French wine industry.

Today, scientists use biopesticides and biological control methods to kill pests. There are several types of biopesticides. Microbial biopesticides contain a bacterium, virus, or fungus that is either in its natural state, or that has been altered by scientists in a lab. These microbes produce a toxin (a poisonous substance) that kills the pest, or they cause a disease in the pest.

Biochemical pesticides are natural substances that interfere with the pest's ability to live normally. For example, substances called pheromones are natural chemicals that insects use to find a mate. Artificial pheromones can interfere with the mating process and slow the pest's ability to reproduce.

Plant-incorporated protectants (PIPs) are pesticides produced by the plant itself. They are created by inserting a gene (a section of DNA that codes for a certain trait) into the plant. The gene causes the plant to produce substances that destroy the pest.

Biological pest control uses the pest's natural enemies to reduce its numbers. Scientists might travel to the country from which the pest originated, bring back its natural enemies, and introduce them into the area in which the pest now lives. Or, they may breed the pest's enemy in a lab to increase its numbers.

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