Spatial and probability distribution of Mexican bean beetle (Coleoptera : Coccinellidae) egg mass populations in dry bean

The spatial pattern and probability distribution of Mexican bean beetle, Ep ilachna varivestis Mulsant. egg masses were studied in four dry bean, Phase olus vulgaris L., fields near Scottsbluff, NE, during the 1994, and 1995 gr owing seasons, Sampling was conducted in a regular and uniform grid to guar antee coverage of the field. The experimental unit in all fields was 0.30 r ow-m, and five measurements were made at 0.76-m intervals. A total of 12,29 0 locations was sampled. Geostatistics and discrete statistics were used to describe the egg mass distribution, Regression was used to detect anti sep arate macroscale trends from the microscale variation, The presence of macr oscale variation indicated a significant edge effect with ovipositing femal es moving into dry bean fields from their overwintering sites. The microsca le variation estimated from the estimated residuals from regressions to est imate trends was studied using semivariograms for all fields. Semivariogram s strongly indicate that Mexican bean beetle eggs are randomly distributed across the field and that this random distribution holds across 10-fold dif ferences in population densities. hs a result of the significant macroscale trends observed, we conclude that egg mass densities may be greater in are as of the field near edges adjacent to beetle overwintering sites, The prob ability distribution that best fit the data was the negative binomial. Our results illustrate the importance of scale in discussing and characterizing distribution. Although there is evidence of edge effect at the field level ? there is no evidence of spatial dependence between egg samples at the sam pling region level. At an even lower Level, the egg mass itself, eggs are a ggregated.