EVALUATION OF ENCARSIA-FORMOSA (HYMENOPTERA, APHELINIDAE) FOR BIOLOGICAL-CONTROL OF SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE) ON POINSETTIA

Biological control of the sweetpotato whitefly, Bemisia tabaci (Gennadius), was undertaken using augmentative releases of the commericially available parasitoid, Encarsia formosa Gahan, on commercial poinsettia (Euphorbia pulcherrima Wild.) stock plant production. Weekly releases of three to five parasitoids per plant were begun soon after the crop was planted (14 April) and continued until the end of poinsettia cutting production (1 September). The effect of E. formosa on the development of B. tabaci was significant on 14 and 16 of 21 weekly sampling dates for adults and immatures, respectively (unpaired t test, P = 0.05). In control cages, there were approximately a 10- and 100-fold greater number of adult and immature whitely populations recorded, respectively, compared with the biological control area. Applications of insectcidal soap were required four times over the 5-mo duration of the trial when the level of whiteflies caught on yellow traps exceeded an a priori threshold level of 10-15 whiteflies per trap. Although a dramatic decrease in the whitefly population was observed in the biological control area, this was not sufficient to prevent whitefly egg deposition of terminal growth, which is the harvestable product. A combination of parasitoid releases, applications of insecticidal soap, the and roguinge infested cuttings were required to produce export-quality cuttings. The strategy of using biolgical control in ornamental crop production is discussed in light of these results.