Abstract
Studies were conducted in 1990 and 1991 to investigate the spatial distribution of counts of western corn rootworm, Diabrotica virgifera virgifera LeConte, adults on yellow sticky traps in field corn. Samples were collected over 3 consecutive wk in July of each year using modified Pherocon A. M. traps placed in a 7 by 7 grid covering 0.84 ha in each of 24 cornfields. Dispersion indices indicated that counts of western corn rootworms on traps were aggregated. Geostatistic analyses, which are based on the relative position of samples, revealed that counts were nonrandomly distributed at least half the time at all population densities. Correlograms showed significant spatial relation in 46 of 72 trap-weeks (63%). Semivariograms, constructed from those 46 trap-weeks, were linear 55% of the time, suggesting the presence of gradients within the sampled portion of each field. The presence and type of spatial pattern was not correlated with mean density. Traps should be placed >30 m apart to obtain counts that are spatially independent.
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