Evaluation of Beauveria bassiana and Beauveria pseudobassiana Against Tanymecus dilaticollis

The grey corn weevil, Tanymecus (Episomecus) dilaticollis Gyll., (Curculionidae: Entiminae) is the most destructive pest of maize and sun flower crops in Romania. In this article we report result of evaluation of native strains of entomopathogenic fungus Beauveria bassiana (Bals.) Vuill. (Deuteromicotina: Hyphomycetes) and B. pseudobassiana Rehner et Humber against Tanymecus dilaticollis (Curculionidae: Entiminae) both in laboratory and field. In laboratory assay, two different strains of B. bassiana and one strain of B. pseudobassiana (BbLy) were applied on insects as 1×108 conidia/ml aqueous suspensions. The pure ATCC 74040 commercial strain of B. bassiana and the commercial mycoinsecticide based on this strain (Naturalis) were included in the laboratory assay for comparison. Adult mortalities were recorded daily, 14 days post-exposure. All the fungal strains have been shown to be pathogenic to T. dilaticollis. The B. bassiana strain (BbTd1) and the B. pseudobassiana strain (BbLy) were effective against adults of T. dilaticollis and comparable in percentage of mycosis and virulence to the B. bassiana strain ATCC 74040. The commercial product Naturalis was superior to the tested fungal strains killing the insects within a day. In the field, the strains BbTd1 and BbLy applied as conidia multiplied on barley grains (1×109 /g d.w) in the soil did not affect the T. dilaticollis density in maize crop.