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Grade 9 Science PESTS AND PESTICIDES BIOACCUMULATION PESTS AND PESTICIDES Pests are organisms that compete with or damage crop species. Examples include weeds, caterpillars, and mice. To maximize the growth of a crop, farmers try to eliminate pests. In nature, there are no such things as pests. All organisms are producers or consumers within food webs. By controlling pests, farmers grow crops in an environment with hardly any consumers or competitors. When farmers plant monocultures, they create ideal environments for pests. If not controlled, pest populations could increase enough to devastate the entire crop. Pesticides are poisons that kill pests. Types of pesticide include herbicides, insecticides, and rodenticides. CHARACTERISTICS OF PESTICIDES Long-lived pesticides persist in the environment for many years. Short-lived pesticides degrade in a matter of days. Broad-spectrum pesticides are toxic to a wide range of pest species. Narrow-spectrum pesticides are toxic to a limited number of species. Pesticides work by causing biological or physical harm to organisms. ISSUES WITH PESTICIDES Pesticide use has many benefits, but also has significant environmental costs. Sprayed pesticides that land on soil or are carried away by the air may become sources of pollution. Pesticides often kill species they were not intended to kill. For example, a broad-spectrum pesticide might kill the predatory insects that feed on pests. Improper use of pesticides, such as spraying at the wrong time of year, can also kill nontarget species. The consequences of non-target killing can be surprising and serious, such as the chain of events that took place on Borneo after spraying DDT to kill mosquitoes. WHAT IS DDT? colorless contact insecticide, toxic to humans and animals when swallowed or absorbed through the skin WHERE IS BORNEO? Borneo is the third biggest island in the world It comprises three countries – Malaysia as well as Brunei on the north side and Indonesia on the south The Dayak tribe are the indigenous people that live there http://www.youtube.com/watch?v=dYXCjENbqSs BORNEO AND DDT In the early 1950s, there was an outbreak of a serious disease called malaria amongst the Dayak people in Borneo. The World Health Organization tried to solve the problem. They sprayed large amounts of a chemical called DDT to kill the mosquitoes that carried the malaria. The mosquitoes died and there was less malaria. That was good. However, there were side effects. One of the first effects was that the roofs of people's houses began to fall down on their heads. It turned out that the DDT was also killing a parasitic wasp that ate thatch-eating caterpillars. Without the wasps to eat them, there were more and more thatch-eating caterpillars. Worse than that, the insects that died from being poisoned by DDT were eaten by gecko lizards, which were then eaten by cats. The cats started to die, the rats flourished, and the people were threatened by outbreaks of two new serious diseases carried by the rats, the plague and typhus. To cope with these problems which it had itself created, the World Health Organization had to parachute live cats into Borneo. DDT AND RACHEL CARSON http://www.youtube.com/watch?v=uARFfWFcV5A &feature=related ISSUES WITH PESTICIDES - BIOACCUMULATION Some pesticides do not break down in the body. If an individual eats food contaminated with the pesticide, it accumulates in the body. The pesticide may continue to accumulate as the organism eats more contaminated food. This process is called bioaccumulation. DDT BIOACCUMULATES UP THE FOOD CHAIN BIOAMPLIFICATION Pesticides that bioaccumulate are soluble in fats and oils, not water. Pesticides stored in the fat of organisms at one trophic level are passed on to consumers at the next trophic level. The higher up the food chain, the more concentrated the pesticides become. This process is called bioamplification. Arctic ecosystems are particularly vulnerable to bioamplification. Many long-lived top consumers live in the Arctic, such as whales, polar bears, and walrus. Inuit living in these environments rely on these species for food. BIOAMPLIFICATION OF MERCURY PESTICIDE RESISTANCE Pest species may become resistant to a pesticide if it is used for a long time. When a pest species develops resistance, farmers need to apply a greater concentration of pesticide, or switch to a different pesticide. Pesticide resistance is a serious concern worldwide.