SPATIAL-ANALYSIS OF COUNTS OF WESTERN CORN-ROOTWORM (COLEOPTERA, CHRYSOMELIDAE) ADULTS ON YELLOW STICKY TRAPS IN CORN - GEOSTATISTICS AND DISPERSION INDEXES

Studies were conducted in 1990 and 1991 to investigate the spatial dis tribution of counts of western corn rootworm, Diabrotica virgifera vir gifera LeConte, adults on yellow sticky traps in field com. Samples we re 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 com rootworms on traps were aggregated. Geostatistic analyses, which a re based on the relative position of samples, revealed that counts wer e nonrandomly distributed at least half the time at all population den sities. Correlograms showed significant spatial relation in 46 of 72 t rap-weeks (63%). Semivariograms, constructed from those 46 trap-weeks, were linear 55% of the time, suggesting the presence of gradients wit hin the sampled portion of each field. The presence and type of spatia l pattern was not correlated with mean density. Traps should be placed >30 m apart to obtain counts that are spatially independent.