THE SOIL BACTERIUM BACILLUS THURINGIENSIS (BT) PRODUCES PROTEINACEOUS INSECTICIDAL TOXINS AND HAS BEEN A MAJOR BIOLOGICAL INSECTICIDE FOR 80 YEARS, SINCE ITS ENTOMOPATHOGENICITY WAS DISCOVERED AT THE TURN OF THE 20TH CENTURY. TRANSGENIC PLANTS EXPRESSING INSECTICIDAL BT TOXINS TO CONFER RESISTANCE TO INSECT PESTS HAVE NOW BEEN WIDELY ADOPTED, PROVIDING SIGNIFICANT ENVIRONMENTAL AND ECONOMIC BENEFITS. HOWEVER, WIDESPREAD APPLICATION OF BT TOXINS HAS IMPOSED INTENSE SELECTION PRESSURE ON TARGET INSECT POPULATIONS TO EVOLVE RESISTANCE TO THE BT TOXINS, AND CASES OF FIELD-EVOLVED RESISTANCE TO BT SPRAYS AND BT-CROPS HAVE BEEN INCREASINGLY REPORTED. CLEARLY, CONTINUING SUCCESS OF APPLICATION OF BT FOR PEST CONTROL REQUIRES CONTINUING DEVELOPMENT OF BT TECHNOLOGIES AND INSECT RESISTANCE MANAGEMENT TACTICS, WHICH CRITICALLY REPLIES ON THE UNDERSTANDING OF DETAILED MECHANISM OF ACTION OF BT TOXINS IN INSECTS. IN THE MECHANISM OF ACTION OF BT TOXINS, THE INTERACTIONS OF BT TOXINS WITH THE INSECT MIDGUT RECEPTORS ARE THE CRITICAL EVENTS DETERMINING THE INSECT KILLING POTENCY OF THE TOXINS, AND CONSEQUENTLY, HIGH LEVEL INSECT RESISTANCE TO BT TOXINS IS OFTEN CONFERRED BY MUTATIONS OF BT RECEPTOR GENES. THEREFORE, THE BT RECEPTORS IN INSECTS ARE CRITICAL DETERMINANTS OF SPECIFICITY AND POTENCY OF BT TOXINS IN INSECTS. HOWEVER, THE FUNCTIONAL ROLES OF THE BT RECEPTORS AND THEIR ASSOCIATED PATHWAYS OF TOXICITY IN INSECTS ARE CURRENTLY NOT WELL UNDERSTOOD, AND IMPORTANT QUESTIONS CONCERNING THE RECEPTOR-MEDIATED PATHWAYS OF TOXICITY WITH BT TOXINS REMAIN TO BE ANSWERED. UNDERSTANDING THE RECEPTORS IN THE PATHWAYS OF TOXICITY OF BT TOXINS IN INSECTS IS AN URGENT NEED. THEREFORE, THIS PROJECT IS DESIGNED TO FUNCTIONALLY DISSECT AND UNDERSTAND THE ROLES OF THE BT RECEPTORS IN THE TOXICITY OF BT TOXINS IN THE CABBAGE LOOPER, TRICHOPLUSIA NI, TO PROVIDE FUNDAMENTAL KNOWLEDGE ESSENTIAL FOR MORE EFFECTIVE INSECT CONTROL WITH BT TOXINS, TO PREPARE FOR THE OCCURRENCE OF INSECT RESISTANCETO BT-CROPS AND TO DEVELOP NEW RESISTANCE MANAGEMENT TACTICS TO SUSTAIN THE ENVIRONMENTAL-FRIENDLY PEST MANAGEMENT PROGRAMS WITH BT.