The alder leaf beetle (Agelastica alni L., Coleoptera: Chrysomelidae) causes approximately 10% of total economic damage to hazelnut product per year in Turkey. A. alni larvae are susceptible to several pathogens indigenous to the area in which these insects occur in Turkey. In the present study, in order to find a more effective and safer biological control agent against this common pest, we evaluated the various biological agents' insecticidal activity during the four hazelnut seasons from 2002 to 2005 on the larvae of the alder leaf beetle collected from the vicinity of Trabzon, Turkey. The tested agents are 25 insect-originating bacteria, 2 bacterial toxins and 1 viral preparation. The results showed that the highest insecticidal activity was obtained by bacterial isolates at 1.8 x 10(9) bacteria/mL dose, within ten days on the larvae of A. alni. These are 90% for Bacillus thuringiensis biovar tenebrionis (4AAI), Bacillus sphaericus (Ar4, isolated from Anoplus roboris L., Col.: Curculionidae), and Bacillus thuringiensis (Mm2, isolated from Melolontha melolontha L., Col.: Scarabaeidae). Our results indicate that these isolates may be valuable as biological control agent.