Practically all of the crops grown by man have important insect pests. Insects inflict damage on plants by their feeding and reproductive activities.
No figures exist for the global damage inflicted on crops by insects but it has been estimated that, for the USA, insects cause an annual loss to crops of about $2 billion, nearly 5% of the potential production. Insects can damage crops directly, or indirectly as vectors of disease. The direct damage can also provide an avenue for bacterial or fungal infection. Examples are the mealy bug and the green spider mite. In the 1970s, these two South American insects were accidentally carried into Zaire and Uganda. Since then they have eaten their way across Africa, destroying up to two-thirds of the cassava crop in some places. To the African, cassava is vital; some 200 million people eat the cassava's large leaves and use its tuberous roots for flour, bread, tapioca, and even alcohol. Without it, the people starve.