Pathogenicity bioassays of isolates of Beauveria bassiana on Rhynchophorus ferrugineus

BACKGROUND:The control ofRhynchophorusferrugineus (Olivier), themainpalmpest in theMediterraneanBasin, is problematicbecause of its biology and the current restrictions inmany European countries on the use of chemical insecticides in urban areas.Entomopathogenic fungi have been studied as potential biological control agents, but information on their natural incidenceis limited. Strains of Beauveria bassiana (Balsamo) Vuillemin were isolated from symptomatic insects collected on dead palms,and their pathogenicity against different instars of R. ferrugineus was evaluated in the laboratory.RESULTS: The overall percentage of infected insects found in Canary palms was 7%. In laboratory bioassays, hatching of eggstreatedwith three different isolates of B. bassianawas 41.2, 26.8 and 29.9%, significantly lower than the control (62.4%). Larvaeand adults were treated with a single isolate in two ways: spraying each insect with a conidial suspension or feeding them withfruit portions previously immersed in the same conidial suspension. At the end of the two trials, the mortality of treated larvaewas 88 and 92%, and themean survival timewas 10.4 and 11.8 days, significantly different fromthe control, where no insect diedduring the trials. Mortality and survival time recorded in either trial on adults did not significantly differ between treatment andcontrol.CONCLUSION: This study shows that the pathogenicity of wild isolates of B. bassiana differs among the tested R. ferrugineusinstars. The low mortality of treated adults supports their use as vectors of B. bassiana as a potential tool for reducingR. ferrugineus populations.