Efficiency of commercial entomopathogenic fungal species against different members of the genus Otiorhynchus (Coleoptera: Curculionidae) under laboratory and semi-field conditions

The application of entomopathogenic fungi against weevils of the genus Otiorhynchus spp. might represent an environmentally friendly management option for biological control of these insects, which have recently increased in their importance as pests in a variety of horticultural plants. As only little information is available on the susceptibility of different weevils of this genus towards various fungal species, laboratory experiments were conducted to evaluate the control potential of three different commercially available entomopathogenic fungi (Beauveria bassiana, Isaria fumosorosea, Metarhizium anisopliae) against adults of O. sulcatus, O. raucus, O. dieckmanni, O. rugosostriatus and O. crataegi. Mortality rates were dependent on fungal and weevil species, respectively. Application of Naturalis((R)) containing B. bassiana as the active ingredient caused a significantly higher mortality rate than evident in control groups in four of the five Otiorhynchus species assessed. Adults of O. rugosostriatus were apparently not susceptible to any of the fungi tested. Efficacy of a single application of Naturalis((R)) against adult O. sulcatus was also assessed in three independent semi-field experiments. Weevils got infected during the first 14 days after application, but mortality rates did not substantially increase until 2 months after application. Even 6 months after application, mortality of weevils was caused by the respective applied B. bassiana strain, which was confirmed via an amplification of isolate-specific microsatellite markers. Thus, a single application of a B. bassiana-based product in the field could have long-term effects on population densities of respective weevils.