Investigation of the population density of the common cockchafer (Melolontha melolontha) in hazelnut orchards of düzce

This study was conducted to investigate population density and distribution of common cockchafer, Melolontha melolontha L. (Coleoptera: Scarabaeidae) causing damage in hazelnut production areas in Düzce province. The study was carried out in 32 hazelnut orchards having different elevations and different locations of Düzce province. M. melolontha larvae were found in 78.12% of the investigated hazelnut orchards. It was determined that the elevation and land characteristics had no effect on the distribution of the pests. Significant difference was not found in population density for coastal, middle and high elevations. M. melolontha density was 1.44 m2 for hazelnut orchards in Duzce province based on the data obtained from 32 orchards. In some of the orchards, pests were no found, but in some orchards, 10 larvae were found per m2. The pest density was fluctuated between 3.00 and 0.22 larvae per m2, depending on the locations. It was determined that the number of pests, in 9.35% of orchards, was found at economic threshold (3 larvae per m2) or above. For the 1st, 2nd and 3rd instar larvae, the average length was 16.14, 25.05 and 37.68 mm, respectively; the average head capsule width was 2.65, 4.22 and 8.54 mm, respectively. As a result of this research, it was determined that population density of common cockchafer was higher than economic threshold for some local areas.