Recent concern on the hazardous effect of chemical pesticides in the environment made scientists consider finding more effective and safer control agents. in future, biological control will be used to control plant pests. Biological agents are isolated from insects or devoloped by using recombinant techniques. There are various techniques to test the insecticidal effects of either pathogens faund naturally in harmful insects (virüs, bacteria, protozoa etc.) or proteins (toxins of Bacillus thuringiensis) or transgenic organisms developed by recombinant techniques on agriculturally important insects. in this article, we attempt to explain the methods used to determine the potential insecticidal effects of biological agents on hazardous insects.