INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Interactions of Alternate Hosts, Postemergence Grass Control, and Rootworm-Resistant Transgenic Corn on Western Corn Rootworm (Coleoptera: Chrysomelidae) Damage and Adult Emergence

Field studieswere conducted in 2003 and 2004 to determine the effects of grassyweeds, postemergence grass control, transgenic rootworm-resistant corn, Zea mays L., expressing the Cry3Bb1endotoxin andglyphosate herbicide tolerance (Bt corn), and the interactions of these factors on western corn rootworm, Diabrotica virgifera virgifera LeConte, damage and adult emergence. Three insect management tactics (Bt corn, its nontransgenic isoline, and isoline plus teßuthrin) were evaluated with two weed species (giant foxtail, Setaria faberi Herrm, and large crabgrass, Digitaria sanquinalis L. Scop), and four weed management regimes (weed free, no weed management, early [V3Ð4] weed management and late [V5Ð6] weed management) in a factorial arrangement of a randomized split split-plot design. In each case, the isoline was also tolerant to glyphosate. Root damage was signiÞcantly affected by insect management tactics in both years, but weed species and weedmanagement did not signiÞcantly affect damage to Bt corn in either year. Adult emergence was signiÞcantly affectedby insectmanagement tactics inbothyears andbyweedspecies in2003,butweed management and the interaction of all three factors was not signiÞcant in either year. The sex ratio of female beetles produced on Bt corn without weeds was generally greater than when weeds were present and thisdifferencewas signiÞcant for several treatments eachyear.Averagedryweightofmale and female beetles emerging from Bt corn was greater than the weights of beetles emerging from isoline or isoline plus teßuthrin in 2003, but there was no difference for females in 2004 and males weighed signiÞcantly less than other treatments in 2004. The implications of these results in insect resistance management are discussed.