Interspecific interactions among natural enemies of Bemisia in an inundative biological control program

Interspecific interactions among insect natural enemies have seldom been investigated experimentally within the context of biological control. Research in this area is needed due to the often contradictory predictions provided by the many theoretical models, the increasing dependence on biological control, and the concern that biological control agents may adversely affect some nontarget organisms. We describe a study whereby the occurrence and dynamics of interspecific interactions among three natural enemies (two parasitoids: Encarsia formosa and Encarsia pergandiella; and one predator Delphastus pusillus) of the whitefly, Bemisia argentifolii (previously referred to as Bemisia tabaci strain ''B''), were evaluated in greenhouse cage experiments. Eight populations consisting of all possible combinations of the three natural enemies and one population of whitefly alone were established to test the following hypotheses: (1) Natural enemy introductions are capable of suppressing B. argentifolii populations; (2) all interspecific interactions are detrimental to achieving biological control; (3) the likelihood of achieving biological control decreases as the potential number of interspecific interactions increases; and (4) the species composition of biological control agents is of greater consequence than the number of natural enemy species released. In addition, we tested the hypothesis (5) that the frequency of interspecific interactions increases with a decrease in host or prey availability. Our results demonstrate that all combinations of natural enemies provided significant levels of whitefly suppression. While the intensities of interspecific interactions among natural enemy species were frequently positively and significantly correlated with the densities of parasitized whitefly, interspecific interactions among natural enemies were not detrimental to achieving higher levels of biological control. The composition of species released, rather than the number of species released, was of greater importance to accomplishing biological control. Releases of D. pusillus in combination with one or both of the parasitoids provided the greatest levels of whitefly suppression. These results suggest that the types of interspecific interactions rather than the numbers of interspecific interactions among natural enemies may be important to the outcome of inundative biological control programs. (C) 1996 Academic Press, Inc.