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Title:The movement behavior and reproductive ecology of western corn rootworm beetles (coleoptera: chrysomeliae) in Bt cornfields with structured and seed blend refuges
Author(s):Hughson, Sarah A
Director of Research:Spencer, Joseph L.
Doctoral Committee Chair(s):Spencer, Joseph L.
Doctoral Committee Member(s):Berenbaum, May R.; Hanks, Lawrence M.; Alleyne, Marianne; Krupke, Christian H
Department / Program:Entomology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Diabrotica virgifera virgifera
Western corn rootworm
Bt corn
Seed blend
Abstract:In the United States, western corn rootworm (Coleoptera: Chrysomelidae; Diabrotica virgifera virgifera LeConte) larvae have been managed using transgenic Bt (Bacillus thuringiensis Berliner) corn hybrids expressing insecticidal Cry proteins since 2003. To slow the evolution of resistance to Cry proteins, the Environmental Protection Agency mandated an insect resistance management (IRM) plan requiring the planting of non-Bt refuges as structured blocks or randomly distributed (seed blends) within Bt cornfields. Refuges allow susceptible larvae to develop without exposure to Cry proteins expressed elsewhere in the field. The modest populations of susceptible beetles from the refuge are expected to disperse across cornfields and mate with most of the rare, potentially resistant, beetles that survived Bt exposure. These “mixed-matings” are expected to produce heterozygous Bt susceptible offspring, delaying resistance because few resistant individuals will have opportunities to mate and produce homozygous Bt resistant offspring. Because the efficacy of the rootworm refuge strategy relies heavily on western corn rootworm movement and mating behavior, it is important to understand these behaviors in Bt cornfields. This dissertation presents data on daily movement within Bt cornfields and details of western corn rootworm mating relevant to resistance management. The spatial and temporal distribution of beetle mating activity and movement were measured in four refuge treatments 1) 20% structured refuge, 2) 5% structured refuge, 3) 5% seed blend refuge and 4) 0% refuge from 2010 to 2012. By testing beetle gut contents for the presence of specific Cry proteins and comparing them to the Cry proteins expressed by plants at their collection site, recent movement could be detected. These findings are presented in Chapters 2 and 3 of this dissertation. In Chapter 2, gut content analysis revealed that 8.5% of mating pairs were mixed-matings: they included a beetle that moved between refuge and Bt corn prior to mating. Most mixed-matings occurred in refuge corn, meaning that most resulted from an individual traveling from Bt to refuge corn before it mated. Dissection of mating females confirmed that most mated while they were newly emerged and that at least 4.5% of females mated more than once in short succession or more than a week after their initial mating. Chapter 3 of this dissertation revealed that the daily proportion of beetles moving between refuge and Bt corn was 17 to 25% collected during the vegetative period but dropped off dramatically to 3 to 10% during the pollination and post-pollination periods. When beetles moved within cornfields, they traveled at a rate of 26 to 31 m/day. In Chapter 4, the effect of high and low beetle density with three different M:F sex ratios (1:3, 1:1 and 3:1) on mating frequency was evaluated. Sex ratio significantly influenced mating regardless of density. More matings per female were recorded in male skewed treatments and more matings by males were recorded in female skewed treatments. Female dissections revealed that matings occurred throughout the five day experiment. Chapter 5 describes a sperm precedence study, in which females were given the opportunity to mate with a new male each day and paternity was assessed for family groups of egg batches as well as the female beetle and her two mates using microsatellite genotyping. Of the females in the study, 8.5% of females accepted a second mate and the mean interval between the first and second mating was 7.5 days. Genotyping results were inconclusive. The assumptions of the high-dose refuge strategy are poorly matched to the reality of western corn rootworm biology. Structured refuges do not facilitate movement and mating patterns that favor production of heterozygous susceptible offspring. A seed blend generated a more even distribution of beetles and mating activity; yet, detailed mating analyses suggest seed blends may not promote more desirable mixed-matings than structured refuges.
Issue Date:2017-07-11
Rights Information:Copyright 2017 Sarah Hughson
Date Available in IDEALS:2017-09-29
Date Deposited:2017-08

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