Ostrinia nubilalis is one of the most damaging of corn pests. It can cause annual economic losses approaching $1 billion in the United States. Resistant corn varieties developed through conventional means have not prevented serious yield losses. High-dose Bt corn hybrids, however, have proven to be very effective against this pest. Some scientists are concerned that resistance may develop with widespread use of Bt corn hybrids. Understanding the mode of inheritance and the mechanism of resistance may help improve strategies to minimize resistance development. A Bt-resistant strain of O. nubilalis has been developed in our laboratory. We would like to identify the genes that are associated with resistance in this strain. Therefore, we have begun to construct cDNA libraries from the guts of Bt-susceptible and Bt-resistant corn borers at three larval age groups: i.e., 6 days, 11 days, and 17 days old. First strand cDNA was synthesized from extracted mRNA and total cDNA was amplified by PCR using a Smart cDNA kit. Competent E. coli cells then were transferred and plated on LB/ampicillin plates. Colonies were individually picked up and cultured overnight in a TB medium. These colonies then were screened by using agarose gel electrophoresis. The inserts of the plasmid DNA of all positive colonies will be sequenced. A microarray technique will be used to compare the gene expression levels between Bt-susceptible and Bt-resistant corn borer strains