BIOLOGICAL-CONTROL OF BEMISIA-ARGENTIFOLII (HOMOPTERA, ALEYRODIDAE) INFESTING EUPHORBIA-PULCHERRIMA - EVALUATIONS OF RELEASES OF ENCARSIA-LUTEOLA (HYMENOPTERA, APHELINIDAE) AND DELPHASTUS-PUSILLUS (COLEOPTERA,COCCINELLIDAE)

Releases of Encarsia luteola Howard and Delphastus pusillus LeConte we re evaluated for their ability to control Bemisia argentifolii Bellows & Perring, n. sp. greenhouse-grown poinsettias. Three treatments, eac h replicated three times, were used to assess the impact of natural en emy releases on B. argentifolii populations: (1) a complete exclusion of natural enemies cage, (2) an identical exclusion cage receiving nat ural enemy releases as a control for cage effects, and (3) releases of natural enemies onto plants within the greenhouse but outside of eith er cage. Weekly releases of the parasitoid E. luteola were initiated t he week the plants entered the greenhouse and three releases of D. pus illus, 1 wk apart, were made when B. argentifolii populations rose dra matically 9 wk into the trial. Release rates for both natural enemies were one insect per plant per week. Weekly collected leaf samples were examined with the aid of a dissecting microscope. The numbers of live whiteflies were recoded by developmental stage as were the numbers of dead (resulting from natural causes, D. pusillus predation, or E. lut eola host-feeding) and parasitized whitefly nymphs. The lack of a sign ificant difference in whitefly densities between the two natural enemy release treatments suggested the absence of a cage effect on whitefly populations. Whitefly densities within the complete exclosure cages w ere significantly greater than the whitefly densities in either of the two natural enemy release treatments, indicating a significant impact of natural enemy releases on B. argentifolii infestations. Whitefly d amage to harvested plants within the natural enemy release areas was n ot significantly different from the damage level observed in the growe r-treated area. The direct cost associated with B. argentifolii biolog ical control ($166.32 per greenhouse section) was almost-equal-to 5 ti mes greater than the insecticide-based B. argentifolii management prog ram currently used by poinsettia growers. This cost differential can b e reduced if the indirect environmental and worker-safety costs associ ated with insecticide use are included, and further reductions should accompany increased commercial availability of D. pusillus.