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Title:Western corn rootworm (Coleoptera: Chrysomelidae; Diabrotica virgifera virgifera LeConte) emergence and abundance in transgenic cornfields with structured and seed blend refuges
Author(s):Hughson, Sarah
Advisor(s):Spencer, Joseph L.
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
western corn rootworm
Bacillus thuringiensis
Bt corn
seed blend
insect resistance management
Abstract:In the United States and Canada, western corn rootworm (Coleoptera: Chrysomelidae; Diabrotica virgifera virgifera LeConte) larvae have been managed using transgenic Bt (Bacillus thuringiensis Berliner) corn hybrids expressing toxic Cry proteins (i.e., Cry3Bb1, Cry34Ab1/35Ab1, mCry3a) for a decade. To delay western corn rootworm resistance to Bt toxins, growers must plant a non-Bt “refuge” in each Bt cornfield. This allows susceptible larvae to develop without exposure to the Bt toxin(s). Matings between susceptible adults and potentially resistant adults developing on Bt plants may delay the development of Bt resistance in their offspring. The refuge strategy relies on the movement of mate-seeking adults from refuge to Bt corn. The research summarized here focused on the distribution of western corn rootworm adults in Bt cornfields planted with structured refuges as blocks at the west end of each plot or as seed blend refuges. The spatial and temporal distribution of western corn rootworm emergence and live collected adults were analyzed in four refuge treatments (20% structured refuge, 5% structured refuge, 5% seed blend refuge and 0% refuge). Abundance was compared across plots and corn phenology stages (vegetative, pollination and post-pollination) from 2010 – 2012. Adult abundance in adjacent soybean fields was also analyzed. Males emerged 6.4 days before females and both males and females emerged from Bt corn 7.3 days after adults from refuge corn plants. In seed blends, emergence from refuge and Bt corn was more synchronous than that of structured refuge treatments. Adult emergence rates (adults/trap/day) from refuge corn in seed blends were significantly lower than those in structured refuge treatments. Adult emergence rates from Bt corn did not differ between structured and seed blend refuge treatments. Adult collection rates in 5% and 20% structured refuge treatments were significantly greater in refuge rows during vegetative and pollination stages. Adults became more evenly distributed across plots during post-pollination. In contrast, adults in 5% seed blend and 0% refuges were evenly distributed across the plots throughout the season. Adults were most abundant in soybeans during the post-pollination phenology of nearby corn plots; few adults were collected in soybeans during vegetative or pollination stages. Most of the adults collected in soybeans each year were female; the percentages were 93%, 88% and 81% in 2010, 2011 and 2012, respectively. The concentration of adults in refuge rows suggest that structured refuge configurations do not generate a distribution of western corn rootworms that facilitate the mixing of adults between refuge and Bt corn. Deploying refuge as a seed blend would serve to delay resistance to Bt technology by producing uniform distributions of western corn rootworms that better promote the mixing of mate-seeking adults between refuge and Bt corn plants.
Issue Date:2013-08-22
Rights Information:Copyright 2013 Sarah Hughson
Date Available in IDEALS:2013-08-22
Date Deposited:2013-08

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