USE OF CUCURBITACIN VIAL TRAPS TO PREDICT CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) LARVAL INJURY IN A SUBSEQUENT CROP OF CORN

Root injury by western corn rootworm, Diabrotica virgifera virgifera L eConte, and northern corn rootworm, Diabrotica barberi Smith and Lawre nce, larvae was evaluated in ten cornfields where adult densities had been monitored the previous August with cucurbitacin vial traps. Traps consisted of 60-ml perforated plastic vials containing an acetate str ip coated with carbaryl and powdered squash with high levels of cucurb itacin, a feeding arrestant. Traps were attached to corn plants at ear height, and the beetles were collected and sexed at various intervals throughout the month of August. For all sampling intervals except the last week of August, female trap capture data explained a significant (P < 0.05) amount of variability in root injury the following summer. In contrast, the only case in which combined male and female trap cap ture explained a significant amount of variability was for the third w eek of August. However, even for this time interval, female trap data explained nearly twice as much variability as did total beetle capture . The best regression equations for predicting larval injury were base d on mean female capture for the entire month of August (R(2) = 0.77, n = 9, P < 0.01), mean female capture for the last 3 wk of August (R(2 ) = 0.73, n = 10, P < 0.01), and mean female capture for the third wee k of August (R(2) = 0.82, n = 10, P < 0.001). This study underscores t he need to develop a trap that captures only female corn rootworms.