Emergence and Beetle Densities of tbe Western Corn Rootworm (Coleoptera: Chrysomelidae): A Comparison Between Rotated and Continuous Cornfields
Meek, David Allen
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Population dynamics of the western com rootworm (WCR) adult beetles, Diabrotica virgifera virgifera LeConte, were studied at three study sites in Northeast Indiana and Southwest Michigan. Each study site contained adjacent continuous and rotated seed cornfields. These sites were studied from mid-July to early September 2001. Two sampling methods, beetle emergence cages, and com-ear-height sticky traps were used to characterize the adult WCR populations. Beetle density and emergence patterns were compared between continuous and rotated fields. We did discover that WCRs emerged from the rotated fields, thus giving support that a new variant of WCRs is present in Michigan as well as in Indiana cornfields. Based on emergence cage data, more beetles emerged from the continuous fields than from rotated fields; however, each study site displayed different population dynamics. We also looked for delays in emergence between the two cropping regimes. Peak emergence and densities occurred for similar sampling, thus suggesting there was no significant delay between adult WCR emergence in the two cropping regimes. This study also compared two types of "sticky traps" used to monitor beetle density. Com rootworm (CRW) traps and Pherecon AM (PAM) traps were placed in all six fields. Mean beetles densities were compared between the traps and no statistical difference was found between the trap types. Overall we did not see emergence levels that were high enough to lead to crop rotation failures that are characteristic of cornfields to the southwest of Michigan. Even though WCR populations were lower in areas of Southwest Michigan compared to other areas of the Midwest, surveying for rootworms must continue to prevent future economic crop loss.