Population dynamics of the western corn rootworm beetle, Diabrorica virgifera virgifera LeConte, were studied in 16 first-year corn (FC) fields and 12 continuous corn (CC) fields in Indiana in 1978–1980. Three sampling methods, corn-ear-height sticky traps, hand collections, and whole-plant beetle counts, were used to characterize beetle populations. Western corn rootworm beetle density, sex ratio, and female ovarial development were monitored from mid-July to October in both cropping sequences. Based on trapping data, a higher density and percentage of female beetles were found in the FC fields than the CC fields after 30 July. Between 7 August and 8 September, a time of significant oviposition, the density of female beetles in FC fields was 2.57 beetles per trap per day, compared with 1.48 in the CC fields. Additionally, the CC fields had a higher total beetle density than the FC fields until 21 August, with the exception of 8 August in 1978 and 7 August in 1979 when the densities were similar. After 21 August, the total beetle density in FC and CC fields was generally not significantly different. Western corn rootworm female beetles collected in FC fields had more ovarial development than did beetles trapped in CC fields on 30 July. Regression equations, predicting whole-plant beetle count economic threshold from larval counts and root damage ratings, indicated that the economic threshold levels used in FC fields should be ca. 50% less than that used in CC fields.
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Godfrey et al. (1983) studied this question.