Determination and pathogenicity of the bacterial flora associated with the spruce bark beetle, Ips typographus (L.) (Coleoptera: Curculionidae: Scolytinae)

The Eurasian spruce bark beetle, Ips typographus (L.) (Coleoptera: Curculionidae: Scolytinae), is one of the most serious pests of spruce trees. We identified 8 bacterial isolates from this pest using conventional bacteriological tests (API 20E and API 50CH strips, and VITEK system (bioMerieux) analysis) and 16S rRNA gene sequence analysis. Based on these studies, all isolates could be identified to the genus or species level as Bacillus sphaericus (It1), Acinetobacter sp.(It2), Kluyvera cryocrescens (It3), Acinetobacter sp. (It4), Vagococcus sp. (It5), Acinetobacter sp. (It6), Proteus vulgaris (It7), and Serratia liquefaciens (It8). We also evaluated the pathogenicity of these bacteria on adults of I. typographus. The insecticidal activity of the bacterial isolates at a concentration of 1.8 × 10^9 bacteria/mL, within 10 days, was 13.3% for B.sphaericus (It1), 16.6% for Acinetobacter sp. (It2 and It4), 23.3% for P. vulgaris (It7), and 53.3% for S. liquefaciens (It8).Since only It8 produced significantly increased mortality relative to the control, the bacterium S. liquefaciens may have potential as a biological control agent against the Eurasian spruce bark beetle.