Virulence of commercial strains of Beauveria bassiana and Metarhizium brunneum (Ascomycota: Hypocreales) against adult Xylosandrus germanus (Coleoptera: Curculionidae) and impact on brood

The ambrosia beetle Xylosandrus germanus (Coleoptera: Curculionidae) is an invasive pest with a wide host range and is a serious pest of orchards and nurseries in the eastern and midwestern US. In this study we evaluated the potential of entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum (Ascomycota: Hypocreales) as control agents against this beetle. Three commercially available strains of these fungi were assayed against adult females to determine their virulence and impact on brood production. Among the three strains tested, B. bassiana Naturalis and M. brunneum F52 were more virulent than B. bassiana GHA. Mortality observed 6 days post-spray was 6.7 +/- 6.7%, 60 +/- 5.8% and 61.7 +/- 7.9% for GHA, Naturalis and F52, respectively, at the highest dosage tested (approximately 600 conidia/mm(2)). Inoculation of adult females did not affect their initial tunneling activity, but resulted in reduced numbers forming galleries and producing brood compared to controls. Broods from treated females were smaller in size, and some had up to 100% of the progeny infected. Infection was observed among all beetle life stages. These data show that the impact of inoculating adult females extends beyond their own survival and suggest that infection of offspring could also significantly affect beetle populations in the field. (C) 2011 Elsevier Inc. All rights reserved.