THE WESTERN CORN ROOTWORM, DIABROTICA VIRGIFERA VIRGIFERA, IS THE MOST SERIOUS PEST OF CORN IN THE US CORN BELT, RESULTING IN OVER $1 BILLION IN LOST YIELD AND MANAGEMENT COSTS EACH YEAR. ONE OF THE PRIMARY TOOLS USED TO MANAGE WESTERN CORN ROOTWORM IS TRANSGENIC BT CORN, WHICH IS GENETICALLY ENGINEERED CORN THAT PRODUCES INSECTICIDAL PROTEIN DERIVED FROM THE BACTERIUM BACILLUS THURINGIENSIS (BT). HOWEVER, IN RECENT YEARS, WESTERN CORN ROOTWORM HAS EVOLVED RESISTANCE TO THREE OF THE FOUR BT TOXINS THAT TARGET THIS PEST (I.E., CRY3BB1, MCRY3A, AND ECRY3.1AB) WITH ONLY ONE BT TOXIN, CRY34/35AB1, STILL SHOWING GENERALLY CONSISTENT EFFICACY AGAINST THIS PEST. IN RECENT YEARS, SOME CASES OF WESTERN CORN ROOTWORM RESISTANCE TO CRY34/35AB1 CORN HAVE BEEN OBSERVED ALONG WITH HIGH LEVELS OF FEEDING INJURY CRY34/35AB1 CORN BY WESTERN CORN ROOTWORM. THE WIDESPREAD EVOLUTION OF CRY34/35AB1 RESISTANCE REPRESENTS A SUBSTANTIAL RISK TO THE CONTINUED EFFICACY OF BT CORN TARGETING WESTERN CORN ROOTWORM. THE GOALS OF THIS PROJECT ARE TO CHARACTERIZE THE EXTENT OF CRY34/35AB1 RESISTANCE WITHIN THE LANDSCAPE BY SAMPLING POPULATIONS OF WESTERN CORN ROOTWORM AND CONDUCTING BIOASSAYS IN THE LABORATORY TO MEASURE THE LEVEL OF BT RESISTANCE. FOLLOW-UP FIELD STUDIES IN AREAS WHERE RESISTANCE HAS BEEN DOCUMENTED WILL BE USED TO BETTER CHARACTERIZE THE EFFECTS OF RESISTANCE ON INJURY TO BT CORN, AND HOW TO BEST MANAGE BT-RESISTANT POPULATIONS OF WESTERN CORN ROOTWORM. LABORATORY STRAINS OF CRY34/35AB1-RESISTANT WESTERN CORN ROOTWORM WILL BE DEVELOPED FROM WESTERN CORN ROOTWORM COLLECTED FROM FIELDS WHERE CRY34/35AB1 RESISTANCE HAS BEEN IDENTIFIED. THESE STRAINS WILL BE USED TO MEASURE THE INHERITANCE OF THE RESISTANCE TRAIT (I.E., DOMINANT VERSUS RECESSIVE) AND WHETHER OR NOT RESISTANCE TO CRY34/35AB1 HAS ASSOCIATED FITNESS COSTS (I.E., WHETHER OR NOT BT RESISTANT INDIVIDUALS ARE LESS FIT IN THE ABSENCE OF BT). BOTH THE INHERITANCE OF RESISTANCE AND WHETHER OR NOT FITNESS COSTS ARE PRESENT WILL PROVIDE CRITICAL INFORMATION ABOUT HOW QUICKLY CRY34/35AB1 RESISTANCE IS EXPECTED TO EVOLVE IN THE LANDSCAPE, AND THUS, HAVING THIS INFORMATION WILL ENABLE BIOTECH COMPANIES AND REGULATORS TO IMPROVE THEIR APPROACH FOR MANAGING RESISTANCE. FINALLY, THIS WORK WILL USE GENOTYPE-BY-SEQUENCING APPROACHES TO IDENTIFY THE GENES ASSOCIATED WITH RESISTANCE. THIS INFORMATION WILL ENABLE MORE EFFICIENT MONITORING OF PEST POPULATIONS FOR RESISTANCE, BY TESTING FOR SPECIFIC GENETIC VARIANTS ASSOCIATED WITH RESISTANCE, AND WILL ENABLE THE DEVELOPMENT OF FUTURE TRANSGENIC TECHNOLOGIES THAT TARGET THE MECHANISMS OF CRY34/35AB1 RESISTANCE. THIS RESEARCH IS ALIGNED WITH PROGRAM AREA 5C: UNDERSTANDING HOW PESTS OVERCOME PLANT PEST RESISTANCE TRAITS CONFERRED BY GENETIC ENGINEERING.