Entomopathogenic Activity of Metarhizium anisopliae Against the Merchant Beetle, Oryzaephilus mercator (Fauvel): A Pest of Stored Date Palm Fruits

Date Palm faces serious challenges due to damage by insect pests, all of which reduce productivity. Attempts to control the insect pests have changed over time from conventional synthetic insecticides to natural control methods such as the use of biopesticides. The 50 adults of O. mercator were each inoculated with one of four different strains of Metarhizium anisopliae (Metsch) Sorok and Beauveria bassiana (F123, IC30, Biob and Bb). The set up was replicated four times. Mortality was recorded daily for 10 days in adults, mortality differed significantly (P < 0.05) within the days of exposure in adults. Biob was the most effective with adult mortality of 94.5% followed by F123, IC30 and Bb with 93%, 84% and 69% mortality respectively and the least mortality was recorded in the control with mortality rate of 40.5%. The dead adults Oryzaephilus mercator were placed in a controlled growth chamber to stimulate the development of fungal mycelia and confirm that the death was caused by infection of the M. anisopliae and B. bassiana isolates. The outgrowth of Metarhizium anisopliae and B. bassiana in all the treatments except control indicated that mortalities of O. mercator were actually caused by the isolates.