Using an assay system developed for the adult silverleaf whitefly, Bemisia argentifolii (Homoptera: Aleyrodidae), insects were exposed to a variety of potential toxins per os. Insects in this assay system were fed through a cellulose mixed-ester membrane on a diet of sucrose and the substance in question. Most of the substances tested in this manner were found nontoxic to this insect. Destruxins, extracted from the entomopathogenic fungus, Metarhizium anisopliae, and the natural insecticide/nematicide Ivermectin were among the few compounds found toxic to adult silverleaf whiteflies.