Resistance development in insect pests against pesticides is one of the most important issues for pest management. Biological control is an attractive strategy for suppressing insects that have become resistant to chemical pesticides. The smaller tea tortrix Adoxophyes honmai (Lepidoptera: Tortricidae) is a serious pest of tea and has acquired resistance to various chemical pesticides, and baculovirus agents have been developed to control this pest in Japan. However, there was great concern about whether A. honmai might also acquire resistance against baculoviruses. To address this question, we developed a model resistant population and studied the mechanism of resistance in A. honmai against baculoviruses. A population of A. honmai that is resistant to nucleopolyhedrovirus (NPV) was selected by exposing a field-collected A. honmai population to the 70% lethal concentration (LC70) of NPV over multiple generations in the laboratory. After 155 generations, the selected strain (Resistant strain; R-strain) showed over 400,000-fold higher resistance to AdhoNPV than the non-selected strain (Susceptible strain; S-strain). In this presentation, mode of resistance of R-strain against baculoviruses were discussed.