Sample density applied to the georeferenced monitoring of defoliating caterpillars in soybean crop/Densidade amostrai aplicada ao monitoramento georreferenciado de lagartas desfolhadoras na cultura da soja

The knowledge of the spatial and temporal distribution of pest insects on soybean crop through the use of precision agriculture tools, have been appointed as an important strategy in the integrated pest management (IPM). In this sense, the objective of this research was to evaluate the influence of sample density in the monitoring of defoliating caterpillars in soybean crop. The experiment was conducted in the experimental area of 47.98ha, located in Julio de Castilhos--RS city, in 2008/2009 season. The georeferenced monitoring was carried out following three regular grids, 50 x 50m, 71 x 71m and 100 x 100m and also following the traditional method of sampling. During the entire crop cycle, and for each grid, there were conducted five evaluations of caterpillar infestations, two on the vegetative stage and three in the reproductive, using a beat cloth. To analyze the spatial and temporal distribution of caterpillars in the area, the data were submitted to descriptive statistical analysis and geostatistics analysis, using semivariograms and kriging to the elaboration of thematic maps. The results obtained indicated that the evaluated sample grids allowed to characterize the spatial distribution of caterpillars and modeled the spatial variability of caterpillars in soybean crop. The sampling and the georeferenced monitoring and further development of georeferenced thematic maps constitute a potential alternative to aggregate to the IPM strategies.