Spatial Distribution of Grape Root Borer (Lepidoptera: Sesiidae) Infestations in Virginia Vineyards and Implications for Sampling

Abstract

Grape root borer, Vitacea polistiformis (Harris) (Lepidoptera: Sesiidae) is a potentially destructive pest of grape vines, Vitis spp. in the eastern United States. After feeding on grape roots for ≍2 yr in Virginia, larvae pupate beneath the soil surface around the vine base. Adults emerge during July and August, leaving empty pupal exuviae on or protruding from the soil. Weekly collections of pupal exuviae from an ≍1-m-diameter weed-free zone around the base of a grid of sample vines in Virginia vineyards were conducted in July and August, 2008-2012, and their distribution was characterized using both nonspatial (dispersion) and spatial techniques. Taylor's power law showed a significant aggregation of pupal exuviae, based on data from 19 vineyard blocks. Combined use of geostatistical and Spatial Analysis by Distance IndicEs methods indicated evidence of an aggregated pupal exuviae distribution pattern in seven of the nine blocks used for those analyses. Grape root borer pupal exuviae exhibited spatial dependency within a mean distance of 8.8 m, based on the range values of best-fitted variograms. Interpolated and clustering index-based infestation distribution maps were developed to show the spatial pattern of the insect within the vineyard blocks. The temporal distribution of pupal exuviae showed that the majority of moths emerged during the 3-wk period spanning the third week of July and the first week of August. The spatial distribution of grape root borer pupal exuviae was used in combination with temporal moth emergence patterns to develop a quantitative and efficient sampling scheme to assess infestations.

Assessing the spatial distribution of Tuta absoluta (Lepidoptera: Gelechiidae) eggs in open‐field tomato cultivation through geostatistical analysis

“…The semivariogram was determined from the log‐transformed sample data to obtain an empirical semivariogram . The empirical semivariogram was used to adjust the best model to fit the theoretical semivariogram . Anisotropic semivariograms were calculated for all datasets in two directions: along (0°) and across (90°) rows.…”

“…39 The empirical semivariogram was used to adjust the best model to fit the theoretical semivariogram. 22 Anisotropic semivariograms were calculated for all datasets in two directions: along (0 ∘ ) and across (90 ∘ ) rows. The adjusted models can be spherical, exponential or Gaussian.…”

“…The spatial distribution of crop pests can provide important information to help determine the locations of their most frequent attacks on crops, their dispersion, and design-monitoring schemes; this information can optimize management programs and reduce insecticide applications. [19][20][21][22] Geostatistical analysis may be applied to investigate the spatial distribution of a crop pest and predict its spread during cultivation. This analysis is a technique for understanding the spatial dynamics of insects and is considered reliable because it incorporates the geographic location of the samples.…”

Effects of Biotic and Abiotic Factors on Grape Root Borer (Lepidoptera: Sesiidae) Infestations in Commercial Vineyards in Virginia

“…Of the environmental factors evaluated, no effect of vineyard proximity to forested areas was observed. Using the same pupal exuviae data, Rijal et al (2014) measured the spatial distribution of infestations. Despite aggregated distributions in blocks with Ն0.5 pupal exuviae per vine, there were no indications that populations were higher or aggregated at the edges of the blocks, although Hoffman and Dennehy (1989) reported higher infestations of grape berry moth, Paralobesia viteana (Clemens), in border rows of the vineyards with wild vines nearby.…”

“…At new vineyard sites, the model may provide a better understanding of the relative risk from this pest and spur the vigilance that is often lacking, but necessary, to mitigate the development of damaging populations at some sites. In combination with this model, the recent development of a quantitative sampling protocol for grape root borer (Rijal et al 2014) and the registration of a mating disruption formulation, have signiÞcantly advanced our capacity to advise eastern grape growers about preventing or managing the ongoing problems associated with this pest. Research on economic injury levels and action thresholds for grape root borer on different grape species and rootstocks and the role of nematodes in its biological control will further enhance the development of integrated pest management recommendations.…”