Pathogenicity of the fungus Beauveria pseudobassiana for Popillia japonica depends on the developmental stage of the insect

• All the four tested B. pseudobassiana strains reduced adult P. japonica survival. • Fungal strains did not reduce larval survival. • Natural B. bassiana and B. pseudobassiana were obtained from field-collected beetles. • Rearing beetles from larvae ensured absence of natural infections. Popillia japonica is an invasive, polyphagous beetle feeding on more than 400 host plants and responsible for major crop damage in infested regions in North America, northern Italy and southern Switzerland. Currently, control of P. japonica largely relies on synthetic insecticides. Recently, Beauveria pseudobassiana has been described as the dominant pathogen on Melolontha melolontha adults, a native scarabaeoid relative of P. japonica . B. pseudobassiana has been detected on several insect species, in soil but also on plant leaves indicating its adaptation to environmental conditions above ground. We evaluated survival of P. japonica adults and larvae exposed to four strains of B. pseudobassiana (ART 2881, ART 2882, ART 2883, ART 2884) and a M. brunneum strain (Ma 43), registered as control agent against several Scarabaeidae species in Europe. All the fungal strains led to a significant three-to-five-fold reduction in the median survival of P. japonica adults, when dipped in conidia suspensions or exposed to fungus inoculated leaves, while ART 2884 was in both tests the most virulent strain. In contrast, none of the fungal isolates reduced larval survival, with mortality rates of 2–8 % after 70 days. From field-collected beetles, we obtained natural Beauveria isolates, some of which were identified as B. pseudobassiana , indicating a possible role of the fungus in natural infection scenarios. The high in vitro virulence of B. pseudobassiana together with its competence for above ground conditions and occurrence on P. japonica in the field indicates potential of this fungus as biological control agent (BCA) against adult P. japonica.