Abstract: Gypsonoma dealbana (Corylus bud moth, Lepidoptera) and Hyphantria cunea (Fall webworm, Lepidoptera) are common pests of Coryllus sp. Up to now, chemical substances have been utilized to control these pests. However, recent concern on the hazardous effect of chemical pesticides in the environment made scientists consider finding more effective and safe control agents. In the present study, in order to find a more effective and safe biological control agent, we tested the insecticidal effects of various biological agents on the larvae of Gypsonoma dealbana and Hyphantria cunea. The tested agents and their insecticidal effects are respectively Autographa californica nuclear polyhedrosis virus (AcNPV, 5 and 25%), Lymantria dispar nuclear polyhedrosis virus (LdNPV, 5 and 25%), Escherichia coli transformed with plasmid containing cryIVA, cryIVD and 20-kDa-protein genes (pHE4-ADR, 17 and 17%) of Bacillus thuringiensis, and toxins isolated from Tenebrionis (BTS-1, 10 and 5%) and Harry Dumagae (HD-1, 31 and 80%) strains of B. thuringiensis. We consider that AcNPV and LdNPV cause the death of larvae through productive infection, however, the rest of the samples cause mortality via cytotoxidity.