Susceptibility, Antioxidant Defense, and Growth Inhibitory Response of Rhynchophorus ferrugineus Olivier (Coleoptera: Curculionidae) against the Virulence of Metarhizium anisopliae Isolates

Rhynchophorus ferrugineus, commonly referred to as red palm weevil (RPW), is an invasive Indian sub-continent pest that infests date palms in the Arabian peninsula and dates-growing countries. In an effort to manage red palm weevil infestations, exotic isolates of entomopathogenic fungi, especially Metarhizium anisopliae were procured from different sources for possible use against red palm weevil larvae. In this study, we evaluated the virulence attributes including the viability and relative hydrophobicity of the spores of M. anisopliae isolates 8453, 7234 and 406; and their impact on the host susceptibility, growth and antioxidant defense. Results indicated that isolate 8453 had 20.64% higher relative hydrophobicity compared with the least virulent isolate 406 that showed the highest LT50 value (10.90 days). The feeding performance experiment revealed significant differences in ECI and ECD indexes. The most virulent isolate 8453 (LT50 = 7.55 days) established in the current study tremendously declined ECI (26.15%) and ECD (39.84%) indexes compared to control treatment larvae. However, the least virulent isolate 406 (LT50 = 10.90 days) could only reduce 7.38% and 12.06% of ECI and ECD indexes, respectively. Furthermore, the virulent isolate 8453 established in the current study successful imparted 100% larval mortality compared with other tested isolates of M. anisopliae. Host antioxidant defense from hemolymph, gut and fat was explored after 24 h of infection by qRT-PCR. The quantification of catalase and peroxidase genes revealed significant differences in their expressions. Overall, the least virulent isolate (406) failed to induce the expression of catalase and peroxidase. However, isolate 8453 greatly induced the expression of studied antioxidant genes. These results indicated that M. anisopliae isolate 8453 seems to be a promising bio-control agent against the infestations of red palm weevils.