Insecticidal activity of Beauveria bassiana against Monochamus alternatus adults

Monochamus alternatus is a major forest pest that spreads pine
wilt disease in pine trees as a vector of pine wilt nematodes. Chemical
insecticides used as fumigants to control overwintering M.
alternatus in forests are highly toxic to the environment, so we
investigated entomopathogenic fungus Beauveria
bassiana ERL836 as an eco-friendly and alternative material to
control overwintering M. alternatus. In this work, we evaluated
the insecticidal activity of B. bassiana ERL836
against M. alternatus adults, the possibility of fungal
colonization on pine tree bark, and finally the control efficacy of fungal
pre-treatment on pine tree logs against emerging M.
alternatus adults in semi-field and field conditions. M.
alternatus adults were killed on the pine trees logs pre-treated
with the B. bassiana ERL836. White conidia were observed
not only on the surface of the dead adults but also on the pine tree logs,
suggesting that the adults were killed by the fungus on the pine. A
formulated ERL836 powder treatment on larvae-infested pine logs showed
high insecticidal activity against adults, similar to that with the fungal
powder suspension treatment, but we demonstrated that using the fungal
powder was simpler than using the suspension in field conditions. Even in
the field condition, the fungal powder treatment showed high insecticidal
activity against M. alternatus adults, which we
attribute to its ability to maintain fungal activity for a long time in
field conditions by covering the pine tree logs with a film during
overwintering. We confirmed that the risk that fungus-infected M.
alternatus adults would spread the fungus to other non-target
forest insects was low. Thus, even a high-concentration treatment in a
specific area is unlikely to transmit the fungus outside that area, so it
can be safely used to control this pine wilt nematode vector in forest
ecosystems.