A bioassay method that uses melon leaves as substrate for eggs and nymphs of the biotype B of Bemisia tabaci (Genn.) was established. Root formation of petioles immersed in tap water guaranteed the turgidity and normal coloration of leaves for a period of 20 to 25 days, enabling the execution of tests with entomopathogenic fungi. The virulence of 50 isolates of Beauveria bassiana (Balsamo) Vuillemin was assessed, as an initial action of a research project that aims the development of a bioinsecticide for controlling Bemisia tabaci nymphs in melon crops. Melon leaves were infested with 18 couples of biotype B adults for 26 hours. First-instar nymphs were selected through microscopic observation approximately 4-5 days after adults removal. Application of fungal isolates was performed with a spray tower. Average number (± SEM) of infective propagules deposited on leaf surface was 1.2x10(4) ± 9.12x10² conidia per cm². For the control it was applied a Tween 80 solution at 0.1%. Three or four replicates were performed per treatment. Incubation was in chamber regulated to 27±1ºC, 70±5% RH and 12 hours photophase. Assessments of dead nymphs were performed at seven and 14 days following spraying. Average mortality in the control treatment was 1.2% at day 14, and 94.4% of the nymphs became adults. Average nymphal mortality at day seven post-spray reached a maximum value of 25.7%. Average mortality at day 14 post-spray varied from 6.1% to 92.3%.
Insecta; silverleaf whitefly; biological control; entomopathogenic fungus
