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 were evaluated for their ability to control Bemisia argentifolii Bellows & Perring, n. sp. greenhouse-grown poinsettias. Three treatments, each replicated three times, were used to assess the impact of natural enemy releases on B. argentifolii populations: (1) a complete exclusion of natural enemies cage, (2) an identical exclusion cage receiving natural enemy releases as a control for cage effects, and (3) releases of natural enemies onto plants within the greenhouse but outside of either cage. Weekly releases of the parasitoid E. luteola were initiated the week the plants entered the greenhouse and three releases of D. pusillus, 1 wk apart, were made when B. argentifolii populations rose dramatically 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. luteola host-feeding) and parasitized whitefly nymphs. The lack of a significant 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 were 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 damage to harvested plants within the natural enemy release areas was not significantly different from the damage level observed in the grower-treated area. The direct cost associated with B. argentifolii biological control ($166.32 per greenhouse section) was almost-equal-to 5 times greater than the insecticide-based B. argentifolii management program currently used by poinsettia growers. This cost differential can be reduced if the indirect environmental and worker-safety costs associated with insecticide use are included, and further reductions should accompany increased commercial availability of D. pusillus.