Pathogenicity of Steinernema carpocapsae ALL Entomopathogenic Nematodes and Their Symbiotic Bacteria as a Biological Control Agent on Red Palm Weevil

Insect-specific pathogens present a sustainable alternative to pesticides for managing the red palm weevil (RPW). This study assessed the efficacy of <i>Steinernema carpocapsae</i> ALL nematodes and their symbiotic bacteria against the third-instar larvae and adults of RPW under laboratory conditions. The symbiotic bacteria were isolated, morphologically characterized, and genetically identified. The results indicated that the mortality rates of RPW larvae treated with <i>S. carpocapsae</i> exceeded 50% in all treatments at 120 h, reaching 93.33% at a concentration of 250 IJs/mL. The morphology of isolated symbiotic bacterium from <i>S. carpocapsae</i> on NBTA medium exhibited a light green color with a glossy surface, a raised center, and a mucilaginous texture. A novel strain of symbiotic bacterium was identified and named as LZ-G7. The bacteria toxicity on RPW adults showed a notable mortality rate of 66.67% at 48 h after feeding with concentration of 10 × 10⁷ CFU/mL. The mortality rate of the third-instar larvae of RPW reached 83.33% after feeding with 0.30 × 10⁸ CFU/g at 96 h and 93.33% after injection into blood cavity with 8 × 10⁶ CFU at 48 h. These results suggest that <i>S. carpocapsae</i> and a novel symbiotic bacterium strain exhibit strong virulence against RPW and have the potential to serve as effective biological control agents in integrated pest management strategies.