Summer cockchafer, Melolontha melolontha (Coleoptera: Scarabaeidae) is one of the most important pests. Up to now, because of hazardous effects of the chemical pesticides have been mostly utilized to control this pest, the development of biological control agents is necessary For this reason, the bacterial flora and viral infection of this insect were investigated, and the insecticidal effects of bacterial arid viral isolate were tested. At the end of the studies, bacteria were identified as Pseudomonas sp. (Mm1), Bacillus thuringiensis (Mm2), Pseudoiumas sp. (Mm3), Enterobacter sp. (Mm4), B. sphaericus (Mm5), Acinetobacter sp. (Mm6) and B. weiheitstephanensis (Mm7). And also, a viral infection was determined. It was identified with microscobic and molecular studies as insect virus belong to entomopoxvirus group. Entomopoxvirus formed the highest insecticidal effect on M. melolontha (93.3%). The highest insecticidal effects in bacterial isolates were formed by B. weibenstephanensis and B. thuringiensis (80%). The viral and bacterial isolates could be utilized as control agent in biological control of M. melolontha.