Plum curculio is a serious pest of tree fruit in the upper Midwest United States. With the passage of the FQPA, there is a need to develop some alternative control strategies in plum curculio management. Esteem (pyriproxyfen) is an insect growth regulator that has been used to control various pests in many areas of world. In this study the effects of Esteem in breaking Northern strain plum curculio diapause has been evaluated. The first series of experiments were based on field applications of the IGR. Cage and sprayed fruit exposure studies were applied with the recommended field rate (141.75g/acre/189.27L per acre). A follow up overwintering study was also performed, using Esteem treated females to assess physiological effects of overwintering. Results from the caged and fruit studies have shown that statistically, the number of oviposition marks for treated and untreated showed no significance. However, dissection data have shown statistically significant difference between the two treatments. The overwintering trial showed no significance in weight loss, but indicated a decrease in the size and number of oocytes and also a visual decline in fat body. Results indicate that Esteem causes early egg development in Northern strain plum curculio, thereby preventing successful overwintering.