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 × 10 ⁹ 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 indigenous B. thuringiensis and B. weihenstephanensis isolates and crystal of B. thuringiensis may be valuable as biological control agents.

In this study, microencapsulation by spray drying was performed to protect spores and crystals of indigenous isolate of Bacillus thuringiensis Se13 from environmental stress. The effects of wall material, inlet temperature, and outlet temperature on microencapsulation of Bt-Se13 were investigated using Taguchi’s orthogonal array. The most suitable wall material determined as maltodextrin DE10. The optimum inlet and outlet temperatures of spray drier were determined as 160 °C and 70 °C, respectively. The number of viable spores, mean particle size, wetting time, percentage of suspensibility and moisture content of the product produced under optimum conditions were determined as 8.1 × 10¹¹ cfu g⁻¹, 13.462 µm, 25.22 second, 77.66% and 7.29%, respectively. As a result of efficiency studies on S. exigua in the laboratory conditions, the LC₅₀ was determined as 1.6 × 10⁴ cfu ml⁻¹. Microencapsulated Bt-Se13 based bio-pesticide may be registered for the control of S. exigua and can be tested against other lepidopterans which share the same environment.