Larvae were collected yearly from 1999-2001 to correlate western corn rootworm (WCR) recovery from maize root systems with that from surrounding soil cores (19-cm diameter and
depth) and to verify that head capsule width is a useful indicator of larval instar in field populations of both WCR and northern corn rootworm (NCR). Maize root systems were
pressure washed to remove surface soil for better standardization of the sampling unit and then dried to maneuver larvae from roots into water traps for collection. Root-surface washes were pooled with corresponding soil cores and stored frozen. Larvae were recovered from each soil core via standard sieving and flotation methods. While fewer WCR were found in maize roots than in soil cores surrounding roots, the two population estimates were significantly correlated (y=3.89x + 16.31, r=0.60, N=81, P < 0.0001), and larvae were vastly easier to sample from roots given the amount of macroorganic matter in our soil cores. Peaks in a frequency distribution of head capsule widths from field grown WCR (N > 800) matched those previously reported by instar for small numbers of mostly laboratory reared specimens. Frequency of head-capsule widths from feral NCR (N > 500) displayed three peaks at sizes similar to those of WCR, but there was some overlap between NCR peaks not seen in WCR.
Species 1: Coleoptera Chrysomelidae Diabrotica virgifera virgifera (western corn rootworm)
Species 2: Coleoptera Chrysomelidae Diabrotica barberi (northern corn rootworm)
Keywords: sampling, corn rootworm
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