Metarhizium anisopliae and Isaria fumosorosea challenge the survival and immunity of the palm weevil, Rhynchophorus ferrugineus Olivier

Aim of study: Rhynchophorus ferrugineus Olivier is an invasive pest of palm worldwide. The use of insecticides by farmers for its management has been found insignificant. This study evaluated the potential use of entomopathogenic fungi for R. ferrugineus management with a particular focus on the fungal infection on the activities of different detoxification enzymes. Area of study: Grubs and adults of R. ferrugineus were collected from various infested date palm fields in the four provinces of Pakistan. Material and methods: Fungi Isaria fumosorosea (If-02) and Metarhizium anisopliae (Ma-M2) were evaluated against R. ferrugineus, and its immune responses were biochemically characterized. Main results: The highest mortality rate was recorded at concentration 3×10⁸ spores mL^-1 on the 7th day post infection in the populations treated with M. anisopliae from Punjab, Khyber Pakhtunkhwa (KPK), Sindh and Baluchistan (93.75, 90.0, 90.0 and 81.25% respectively). M. anisopliae with lowest LC₅₀ (1.1×10⁶ spores mL^-1) from Sindh also proved to be the most lethal fungus against R. ferrugineus. Maximum acetylcholinesterase (AChE) and glutathione S-transferases (GSTs) activities were observed in Baluchistan (26.28 and 24.0 μmol min^-1 mg^-1 protein, respectively) and maximum esterases (EST) activity (35.4 μmol min^-1 mg^-1 protein) was observed in the KPK population on the 3rd-day post I. fu-mosorosea infection. Research highlights: Fungal infection by I. fumosorosea caused a significant increase in AChE, GST and EST activities which may hinder R. ferrugineus development. However, M. anisopliae, to some extent, also inhibited enzyme activities and yielded a sudden increase in mortality. Future bio-pesticides could be developed for integrated pest management (IPM) of palm weevil.