Kevin Snyder, age 13, of Haggerstown, Md., for his question:

WHAT IS DDT?

DDT is a chemical preparation that has been used for destroying pests such as mosquitoes or flies. You can understand why it is simply called "DDT" when you learn that its full name is a 31 letter word: dichlorodiphenyltrichloroethane.

In 1973, DDT was banned in the United States except for possible use in extreme health emergencies.

A Swiss chemist named Paul Muller was given the Nobel Prize in 1939 for recognizing DDT as a potent nerve poison on insects. It was heavily used as a pesticide during World War II prior to jungle invasions. After the war it was used widely in all parts of the world to fight yellow fever, typhus, malaria and other insect spread diseases.

In the 1960s suspicion grew that DDT entered the food chain and eventually caused reproductive dysfunctions, such as thin eggshells in some birds. Since the U.S. banned DDT in 1973, many other nations have also banned it or put it under strict control.