Abstract: Nonsteroidal ecdysteroid agonists act in a similar fashion with ecdysone to affect the insect pest larval molting. The ecdysone receptor is so sensitive and specific that the new screening assay technique must be set up to detect the activity of insecticidal lead compounds. In this study, the functional domains of the ecdysone receptor and ultraspiracle protein from Spodoptera litura were cloned by RT-PCR. These two fragments were inserted into expression vectors and named as pEHISEGFPTEV-EcR_cde and pEHISEGFPTEV-USP_cde, respectively, and the fusion proteins were purified after induction. With l mg/mL fusion protein and 8 nmol/L ³H-PonA, the radioligand receptor binding assays were carried out to detect the radioactivity changes in the count per minute (CPM) in treatments with four insecticides (tebufenozide, fufenozide, dibenzoylhydrazide and chlorbenzuron) at different concentrations. The results showed that when the concentrations of tested compounds gradually increased, the CPM of the first three insecticides was reduced in different degrees. Tebufenozide had the highest degree of radioactivity reduction, followed by fufenozide and dibenzoylhydrazide, while the radioactivity of chlorbenzuron had almost no change. This study indicated that among the tested four insecticides, tebufenozide has the highest insecticidal activity under the same conditions, and the method can be used to preliminarily screen out the insecticidal activity of nonsteroidal ecdysteroid agonists or lead compounds.

Key words: Spodoptera litura; ecdysteroid receptor (EcR), ultraspiracle protein (USP), prokaryotic expression, count per minute (CPM)