The hazelnut beetle (Balaninus nucum L., Coleoptera: Curculionidae) is the single greatest source of damage to hazelnut fruits throughout the world. It causes approximately 30-40% of the total economic damage to hazelnut products per year in Turkey. In this study, we investigated the bacterial flora of the hazelnut beetle collected from the vicinity of Trabzon (Turkey) during 1995-1997 and tested them for insecticidal activities. The number of total bacteria in larvae (1.8 x 10(9) cell/larva) and adults (1.41 x 10(11) cell/adult) was identified. Based on colony colour and morphology, five isolates were identified. According to morphological, physiological, biochemical and molecular characters of the isolates, they were identified as Bacillus thuringiensis, Pseudomonas fluorescens, Micrococcus luteus, Serratia marcescens and Escherichia coli. The insecticidal activities of these bacterial isolates on third-stadium larvae of B. nucum were investigated. The highest insecticidal effect determined on B. nucum within three days was 100% with S, marcescens. The effects of the rest of the isolates are 45% for B. thuringiensis, 20% for P. fluorescens, 30% for M. luteus and 25% for E. coli.