Susceptibility of Sitophilus zeamais (Mostch.) (Coleoptera: Curculionidae) to Beauveria bassiana and Metarhizium anisopliae

Evaluation of eleven Metarhizium anisopliae and six Beauveria bassiana isolates against the maize weevil Sitophilus zeamais was conducted under laboratory with the objectives of identifying the most virulent locally available fungal isolates, and determining the dose mortality response. The pathogenicity (virulence) of the entomopathogenic fungi was determined using LT50 and percent mortality at the conidial concentration of 1 x 108 ml-1. The most virulent isolates of M. anisopliae (PPRC-2, PPRC-14 and PPRC-51) and B. bassiana (PPRC-GG and PPRC-HH) caused 84.4% to 98.3% mortality to S. zeamais. These isolates had LT50 ranging from 3.8 to 4.3 days. The dose response study with the isolates PPRC-2, PPRC-14 and PPRC-51 at doses ranging from 1x 104 to 1x 108 conidia  ml-1  revealed susceptibility of the S. zeamais with mortality ranging from 25 to 95.5%. There was an increase in the resulting LT50 from 4.0 to 11.9 days with a decrease in conidial concentration from 1x 108 to 1x 104 conidia ml-1. PPRC-2 showed the lowest LC50 (1.46x 10 conidia ml-1) followed by PPRC-14 and PPRC-51 (3.5x 105 and 3.9x 105 conidia ml-1, respectively). In conclusion, the isolates PPRC-2, PPRC-14, PPRC-51, PPRC-GG and PPRC-HH, can be considered as a potential candidates in the development of mycoinsectisdes against S. zeamais.