Dusky sap beetles (Coleoptera : Nitidulidae) and other kernel damaging insects in Bt and non-Bt sweet corn in Illinois

Bt and non-Bt sweet corn hybrids (Rogers 'Empire' Bt and non-Bt, respective ly) were compared for distribution of kernel damaging insect pests in centr al Illinois in 1998 and 1999. The occurrence and damage by caterpillars [pr imarily Helicoverpa zea (Boddie)] were reduced by at least 80% in each year for the Bt compared with the non-Bt hybrid. However; the incidence of sap beetle adults (primarily Carpophilus lugubris Murray) was higher, and larva e, lower for the Bt versus non-Bt in 1999. The incidence of ears with more than five kernels damaged by sap beetles was higher for the Bt compared wit h non-Bt hybrid in 1998 (13.8 versus 5.5%), but nearly equivalent in 1999 ( 15.3 versus 15.1%, respectively). Distribution of predators on plants (prim arily Coccinelidae) and harvested ears (primarily Orius spp.) were not sign ificantly different on Bt versus non-Bt hybrids. Ears with husks hush with the ear tip or with ear tips exposed had significantly higher sap beetle da mage for both hybrids, and the Bt hybrids had significantly higher incidenc e of exposed ear tips in both years. Sap beetle numbers determined by scout ing were often proportional to numbers of beetles captured in baited traps, increasing and decreasing at about the same time. However, values determin ed with traps were typically less variable than when scouted, and time of s ampling was typically four times more rapid for each trap than for each 10 giant scout sample when measured in 1999.