B. WADE FRENCH
Northern Grain Insects Research Laboratory, USDA–ARS, 2923 Medary Ave., Brookings, SD, U.S.A., 57006
L.D. CHANDLER
Red River Valley Agricultural Research Center, USDA-ARS, 1307 North 18th Street, Fargo, ND, U.S.A., 58105

The use of transgenic maize may soon be a reliable substitute for insecticides as a control tactic for corn rootworms (CRW). However, resistance among CRW could quickly evolve thereby diminishing the durability of the transgenic maize. To counteract the spread of resistance, refugia (non-transgenic maize) probably will be planted to sustain non-resistant CRW numbers. To keep resistant numbers low, gene flow among resistant and non-resistant CRW populations must occur. Dispersal is a means by which gene flow occurs among populations. Our goal is to examine the dispersal and reproductive biology of the western and northern CRW under field conditions. With respect to CRW movement, we wish to estimate the dispersal potential of western and northern CRW across the landscape in relation to sex, size, and reproductive status. Our study location is in the South Dakota CRW areawide management site. Using sticky traps, we captured 2460 northern CRW and 1116 western CRW dispersing between fields of continuous maize, first year maize, and soybean. Peak dispersal occurred in August for western CRW and August through September for northern CRW. Most CRW were captured between continuous and first year maize fields and at canopy height. Also using sticky traps attached to the top of conduit poles to detect vertical flight, we captured 805 northern CRW and 45 western CRW. More northern CRW were captured emigrating from maize fields than immigrating into maize fields. We found no differences in the number of western CRW immigrating and emigrating from maize fields. The number of western CRW was extremely low and may not be indicative of their migratory behavior into and out of maize fields.