Histopathological Effects of the Entomopathogenic Fungus Metarhizium anisopliae (Metschnikoff, Sorokin) on Adults of Rastrococcus invadens, (Williams, 1986)

The mealybug (Rastrococcus invadens), is a major pest of mango trees, causes extensive damage and significant yield losses in Senegal. The control methods used seem less effective. Mechanical control is the most widely used method in some regions of Senegal. However, the use of natural products has shown promising potential. The aim of this study was to investigate the pathogenicity of Metarahizium anisoliae on adults mealybugs (Rastrococcus invadens) and to assess the resulting histological damage. Under laboratory conditions (75% relative humidity and 27°C), we tested oil-based formulations of Metarhizium anisopliae conidia at doses of 10³, 10⁴, 10⁵, 10⁶, and 10⁷ spores/ml to mango leaf discs infested with adult Rastrococcus invadens. Treated insects were examined using optical microscopy with histological techniques to observe tissue damage. The results revealed that mortality rates were higher 48 hours after application, with respective rates of 37.4±8.8%, 58.6±5.22%, 75.45±5.28%, 92.35±1.69%, and 100±0.01% compared to the control group at 2.4±1.2%. Histological sections showed a progressive invasion of fungal spores through the cuticle, leading to the destruction of fatty tissues, muscles, and wax glands, followed by internal proliferation. These findings suggest that entomopathogenic fungi such as M. anisopliae can be used and popularized as biopesticides in the management of R. invadens.