Geostatistical analysis of the attractive distance of two different sizes of yellow sticky traps for greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Homoptera: Aleyrodidae), in cherry tomato greenhouses

Variogram analysis was used to estimate and compare the attractive distances of two different sizes of yellow sticky traps (small trap: 9.6×8.0cm; large trap: 9.6×16cm) for sampling greenhouse whitefly, Trialeurodes vaporariorum (Westwood), adults in four commercial cherry tomato greenhouses, during 2002-2003. The patch size of T. vaporariorum immatures between plants was also estimated using visual counts. Within each greenhouse, 64 permanent sampling stations were established on an 8×8 grid, with one yellow sticky trap or one tomato plant per location. Standardised exponential and Gaussian variogram models were fitted to the empirical variograms developed from the data collected by each sampling method. All the variograms reached the sill indicating the presence of spatial dependence among the spatial data obtained by the two sampling methods. For T. vaporariorum adults on sticky traps the range of variogram (a measure of attractive distance) was not considerably different between the two trap sizes: 15.40 and 15.95m for the large and small traps, respectively. This result indicated that the attractive distances of the two different yellow sticky traps were very similar. The ranges of the variograms for the visual count of immatures on plants were always less (7.49-10.00m) than those for adults, indicating that the attractive distance of the traps for T. vaporariorum adults extends beyond the patch size for immatures on cherry tomato plants. These data have implications for developing sampling plans for the management of T. vaporariorum in tomato greenhouses.