Determining spatial distribution of alfalfa leaf weevil Hypera postica and root weevils Sitona spp. (Coleoptera: Curculionidae) using geostatistics

In this study, spatial distribution pattern of alfalfa leaf and root weevils was determined using geostatistics. This study was conducted in four alfalfa fields (0.4, 0.5, 3.1 and 7.3 ha) located in the experimental farm of Faculty of Agriculture University of Tabriz, Tabriz, Iran. The 0.4 and 0.5 ha fields were divided into 10 × 10 m grids and 3.1 and 7.3 ha fields were divided into 30 × 30 m grids. Weekly samplings were started at the end of winter and continued until the last clipping of the yield. Depending on the height of alfalfa plants, a 1 × 1 m quadrat and a standard sweep net were used for weevils sampling. One sample was taken from each grid. Spatial analyses of data were conducted using GS 5.1.1. Degree of dependence (DD) was used for determining spatial dependency of data and spatial distribution pattern of alfalfa weevils. Distribution maps were produced using ArcGIS 9.3. DD values were > 26% for 97 out of 116 data series, indicated that weevils are aggregately distributed in the alfalfa fields and has medium to strong spatial dependency. These results provide useful information about ecology of leaf and root weevils in the alfalfa fields and can be used in site-specific management programs.