Laboratory bioassays were conducted to evaluate the sublethal effects of fenpyroximate and pyridaben on life-table parameters of two predatory mites species, Neoseiulus (= Amblyseius) womersleyi and Phytoseiulus persimilis. In these assays, young adult females were treated with three sublethal concentrations of each acaricide. The life-table parameters were calculated at each acaricide concentration, and compared using bootstrap procedures. For each acaricide, the LC(50) estimates for both species were similar, yet the two species exhibited completely different susceptibility when the population growth rate was used as the endpoint. Exposure to both acaricides reduced the net reproduction rate (R (o)) in a concentration-dependent manner and their EC(50)s were equivalent to less than LC(7). Two different scales of population-level endpoints were estimated to compare the total effect between the species and treatments: the first endpoint values were based on the net reproductive rate (fecundity λ) and the second endpoint values incorporated the mean egg hatchability into the net reproductive rate (vitality λ). The fecundity λ decreased in a concentration-dependent manner for both acaricide treatments, but the vitality λ decreased abruptly after treatment of N. womersleyi with pyridaben. The change in the patterns of λ revealed that the acaricide effects at the population level strongly depended on the life-history characteristics of the predatory mite species and the chemical mode of action. When the total effects of the two acaricides on N. womersleyi and P. persimilis were considered, fenpyroximate was found to be the most compatible acaricide for the augmentative release of N. womersleyi after treatment.
Variogram analysis was used to estimate and compare the attractive distances of two different sizes of yellow sticky traps (small trap: 9.6 ¥ 8.0 cm; large trap: 9.6 ¥ 16 cm) 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 15.95 m 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 (7.49-10.00 m) 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.
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