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The entomopathogenic bacterium Bacillus thuringiensis is the most widely used biopesticide. In this study, to find and identify the more toxic B. thuringiensis strains against coleopteran pests, we isolated a B. thuringiensis strain (Xd3) from European shot-hole borer, Xyleborus dispar (Coleoptera: Scolytidae), a higly damaging pest of hazelnut. Based on various morphological, physiological, biochemical, and molecular characteristics, the bacterial isolate was identified as B. thuringiensis subsp. tenebrionis (morrisoni) serovar H8a8b. This isolate was compared with the reference strains by scanning electron microscopy, SDS-PAGE analysis, cry gene content, and insecticidal activity. Isolate Xd3 forms a flat-square inclusion containing a protein component of c. 70 kDa. PCR analysis showed that the Xd3 has a cry gene, cry3. Toxicity tests were performed against coleopteran species. One hundred percent mortality was observed against larvae of Agelastica alni (Coleoptera: Chrysomelidae). The others were 90% for Amphimallon solstitiale (Coleoptera: Scarabaeidae), and Melolontha melolontha (Coleoptera: Scarabaeidae). Our results indicate that B. thuringiensis subsp. tenebrionis (Xd3) may be valuable as biological control agent for coleopteran insects.

Melolontha melolontha larvae are susceptible to several pathogens indigenous to the area in which these insects occur in Turkey. We isolated and identified seven bacterial strains from M. melolontha and evaluated their pathogenic activity during three hazelnut seasons from 2002 to 2004 on larvae of M. melolontha. Using various morphological, physiological, and biochemical characteristics in detail, bacterial isolates were identified as Pseudomonas sp., Bacillus thuringiensis, Pseudomonas sp., Enterobacter sp., B. sphaericus, Acinetobacter sp., and B. weihenstephanensis. The insecticidal activity of isolates at 1.8 × 109 bacteria/ml dose, within 10 days on the larvae of M. melolontha are 40% for Pseudomonas sp., 80% for Bacillus thuringiensis, 50% for Pseudomonas sp., 20% for Enterobacter sp., 60% for B. sphaericus, and 80% for B. weihenstephanensis. We also purified crystals from B. thuringiensis and B. sphaericus and tested the insecticidal activity on the larvae of M. melolontha. In crystal protein bioassays, the highest insecticidal effect detected was 70% with crystals of B. thuringiensis. Our results indicate that indigenousB. thuringiensis and B. weihenstephanensis isolates and crystal of B. thuringiensis may be valuable as biological control agents.