Control of rice weevil (Sitophilus oryzae L., Coleoptera: Curculionidae) with various formulations of Metarhizium anisopliae

Formulations of Metarhizium anisopliae conidia with oven ash, chalk powder, charcoal and wheat flour at a ratio of 1:4 (W/W) were prepared. Formulations containing charcoal and oven ash had a conidial viability half-life of 4.1-4.3 months at 20 +/- 1degreesC. In comparison, unformulated conidia held under the same conditions had a viability half-life of 0.9 month. Bioassays carried out at 28 +/- 2degreesC and 70 +/- 5% RH indicated that the treatments with charcoal and oven ash formulations at a rate of 2.0% or 2.8 mg/cm(2) of treated area resulted in 73.3-86.7% mortality of adult Sitophilus oryzae after 7 days when treatments were applied before or after pest infestations. Mortality in F1 adults was 28.9-47.5% when exposed, upon emergence, to the same formulations previously applied against their parents. Treatments applied before pest infestation with charcoal or oven ash formulation reduced damage rates to wheat grains to 0.5% compared to the control (6.0%). Development time of S. oryzae was prolonged 4-8 days when the grains were treated before pest infestation with fungal formulations in charcoal or oven ash. A synergistic effect between the fungus and the most effective dusts, charcoal or oven ash, for the "after pest infestation" treatments was obtained during bioassays for evaluation of S. oryzae adult mortality. Additional experiments are required to explain the mechanism of this synergism. (C) 2003 Elsevier Ltd. All rights reserved.