Encarsia formosa Gahan is used worldwide for commercial control of whiteflies in greenhouse crops. Commercial use began in Europe in the 1920s, but by 1945 interest waned due to the development of pesticides. After 1970, use was reinitiated and has expanded from 100 hectares of greenhouse crops to 4800 hectares in 1993 (van Lenteren and Woets, 1988; Hoddle et al., 1998).