Efficacy of Metarhizium Anisopliae Combined With Diatomaceous Earth Against Sitophilus Oryzae (Coleoptera: Curculionidae) Under Laboratory Conditions

Abstract

The objective of the present study was to assess the efficacy of an indigenous isolate of Metarhizium anisopliae alone and with diatomaceous earth (DE) formulation against the rice weevil, Sitophilus oryzae (Coleoptera: Curculionidae). Rice grains were admixed with three doses of M. anisopliae, i.e., 2.78 x 10⁶, 2.78 x 10⁷ and 2.78 x 10⁸ conidia kg^-1 alone and in combination with DE Protect-It^TM applied at the rate 100 and 200 ppm, respectively. The weevil's mortality was determined after 7, 14 and 21d of exposure intervals at 25 ± 2 °C and 55% R. H. After each mortality count, the dead adult insects were removed and after the last exposure interval, the treated material was kept for the following 62d to check the progeny production. Rice grains treated with the highest dose rate of M. anisopliae combined with 200 ppm of Protect-It^TM provided the maximum mortality and reduced progeny production of S. oryzae. These findings suggest that the combined application of entomopathogenic fungi and DE is more effective than when applied singly against S. oryzae. Moreover, it was also observed that the low doses of M. anisopliae showed the highest rate of mycosis and sporulation in the dead adults of S. oryzae.