ACTIVITY OF NATURAL TOXINS AGAINST THE SILVERLEAF WHITEFLY, BEMISIA-ARGENTIFOLII, USING A NOVEL FEEDING BIOASSAY SYSTEM

An assay system was developed for the adult silverleaf whitefly, Bemis ia argentifolii Bellows & Perring (Homoptera: Aleyrodidae). This pract ical device was constructed from standard disposable laboratory materi als. Whiteflies were harvested directly from the leaf and into a colle ction vial by vacuum aspiration, minimizing physical damage to the ins ect. Insects were fed through a cellulose mixed-ester membrane on a di et of 20-27% sucrose alone or sucrose in an extract of zucchini (Curcu rbita moschata Duchense). Mortality and honeydew production were score d. At 22-25 degrees C and 50-55% relative humidity, control mortality generally remained at or below 15% during a 48 h assay period. The bio assay system was first tested using the insecticide, Imidacloprid, the n used to screen a number of natural products with potential insectici dal activity against the whitefly. Destruxins extracted from the entom opathogenic fungus, Metarhizium anisopliae, and the natural insecticid e/nematicide, Ivermectin, as well as bee venom and two of its componen ts, melittin and phospholipase A(2), were found to be toxic to B. arge ntifolii. Five lectins, Bacillus thuringiensis toxins, gossypol, an ex tract of Paeciliomyces fumosoroseus, wasp and scorpion venom, and a tr ypsin inhibitor were not found to be insecticidal to adult B. argentif olii.