Orange, grapefruit, lemon and lime orchards are being wiped out across Florida from a plague called citrus greening disease. A team of scientists from Washington State University in Pullman is studying the bacterium that causes the condition. They hope to find a cure. David Gang, a biological chemist at Washington State University, said the bacterium that causes greening disease is transmitted by a psyllid , a winged insect about half the size of a fruit fly, which spreads it from tree to tree.