Agricultural officials ordered 750 fruit fly traps set out in central Los Angeles after a melon fly was found at the downtown produce distribution center. "We are taking the discovery . . . very seriously," Los Angeles County Agricultural Commissioner Paul Engler said. An infestation of the flies could cause serious problems with fruit and vegetables, Engler said. The melon fly, whose potential for damage is said to be as serious as that of the Mexican and Mediterranean fruit flies, is generally found in Hawaii and Southeast Asia. One baby melon fly was found in Pasadena last June.