Identification and evaluation of a new entomopathogenic fungal strain against Riptortus pedestris (Hemiptera: Alydidae) and its two egg parasitoids

Abstract

A strain (ARP14) of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin was isolated from field-collected Riptortus pedestris (Fabricius) (Hemiptera: Alydidae). The lethal median concentration of the ARP14 strain was compared with that of a commercialized strain (GHA) of the same fungus against R. pedestris and its two egg parasitoids, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Platygastridae). Mortality and mycosis rates were evaluated after exposure to five concentrations of the fungus, i.e., 1×10 ⁹, 1×10 ⁸, 1×10 ⁷, 1×10 ⁶, and 1×10 ⁵ conidia/mL, using a glass scintillation vial as an exposure arena in 25.0 ± 0.5°C and 93.7 ± 2.9% RH. The lethal median concentrations (LC ₅₀) for 2 ^nd and 4 ^th instar nymphs, and adults of R. pedestris were not significantly different between the two strains of B. bassiana. However, the mycosis rate of ARP14 was 1.3 and 1.8 times higher than that of the GHA strain in 4 ^th instar nymphs and adult females of R. pedestris, respectively, at the 1×10 ⁸ conidia/mL concentration. More interestingly, the mycosis rates at 1×10 ⁸ conidia/mL concentration in the parasitoids G. japonicum and O. nezarae were much lower in the ARP14 strain (15.0 and 0%) than in the GHA strain (73.3 and 66.0%), respectively, suggesting that the B. bassiana strain ARP14 is less virulent to these parasitoids than the commercially available strain. Our results suggest that B. bassiana ARP14 may be a potential new biopesticide against R. pedestris with fewer negative effects on beneficial parasitoids than currently available options.