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Biological control

created Oct 18th 2018, 17:26 by ShobhitRaj1592559


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314 words
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Biological pest control uses a natural enemy of the pest to keep its numbers down. A good example occurred in  Australia in the 1920s and 1930s. A cactus called prickly pear was brought to Australia from America in the 1920s. lIt quickly established itself in Australia and became a weed pest.  
It grew so fast that large areas became thickly covered with the cactus and could not be used for farming. Removing the cactus with weedkillers or by digging it up would have been very expensive. Scientists, therefore, began looking for ways of controlling the cactus biologically. Eventually, they discovered a moth, Cactoblastis cactorum, which lays its eggs on the prickly pear cactus. When the caterpillars hatch out, they eat away at the cactus. If there are enough caterpillars, they eventually destroy the cactus. Millions of eggs of the moth were released onto the cacti by farm workers. The operations were so successful that within five years most of the cacti had been destroyed. After all the cacti had disappeared, the caterpillars died out. This was important because they might have turned to another source of food, and perhaps started eating food crops.
In many ways, biological control is safer than chemical control. is safer than chemical control. It does not involve introducing toxic chemicals into the environment. Nevertheless, biological control can go wrong. A food web is a very complicated network of relationships between different organisms. Interfering with one part of the web can have unexpected effects in other parts.  
The house sparrow was deliberately introduced into New Youk from Britain in the hope that it would eat caterpillars that were damaging elm trees in public parks. Unfortunately, the sparrows were rather poor at hunting caterpillars in trees. Instead, they looked for food elsewhere and soon spread to agricultural land outside NewYork. The birds that were meant to control pests became pests themselves.

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