Laboratory Evaluation, 1988

Abstract

The fungus Beauveria bassiana (Balsamo) Vuillemin was obtained from Abbott Laboratories, North Chicago, 111. The technical powder contained 1 x 1010 conidia/g (ABG 6178, lot 76-015-BR). A wetting agent, Tween-100 (0.05% concentration) was used to prepare suspensions of B. bassiana. A laboratory strain of boll weevils was used in these evaluations. The bioassay procedures used to evaluate the pathogenicity of this entomopathogen consisted of topical treatment of pupae and adults. Pupae (12 mg each) in the white-eyed stage were removed from the larval rearing diet, surface rinsed with 0.1% sodium hypochlorite, and air dried. The pupae were dipped in aqueous suspensions of B. bassiana and placed in 30-ml paper cups that contained moist filter paper and then held at a temperature of 78°F. Controls were dipped in water only and similarly handled. Adults (4-6 d old) were dipped in the suspensions, air dried, and held in Petri dishes at 78°F. A 5% sucrose solution was provided to the adults and changed daily. Ten concentrations of B. bassiana, ranging from 101 to 1010 conidia/ml, were evaluated. Microscopic examinations were made. Dissections were performed on pupae and adults to determine internal growth of mycelium. The percent ± SEM mortality inflicted by B. bassiana was then calculated.