-Insects and other pests cause immense amounts of damage to crops each year, greatly reducing yields. This can be a particular problem in developing counrties, where it contributes to food shortages.
-Pesticides are chemicals that kill pests. Insecticides and fungicides are widely used. They may be specific (killing only the pest species) or broad-spectrum (killing many different species). There are few specific pesticides, and they tend to be very expensive.
-In developed countries, there are strict regulations about the amount of pesticide traces that may be present on food offered for sale. Many pesticides used in the past have now been banned, as evidence emerged of thier possible harmful effects on human health.
-In the past, widespread use of persistent insetides such as DDT and dieldrin led to thier bioaccumulation, and subsequent damage to organisms at the top end of food chains. These are no banned in many countries, but are still used in some developing countries as the only practible and affordable method of controlling malaria and other insect-borne diseases.
-Natural selection may produce strains of the pest that are resisitant to a pesticide.
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