Location: Pest Management and Biocontrol Research
Title: Sequential sampling plans for estimating censity of glassy-winged sharpshooter, homalodisca vitripennis (Hemiptera: Cicadellidae) on citrus Authors
Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 5, 2010
Publication Date: November 20, 2010
Repository URL: http://handle.nal.usda.gov/10113/46606
Citation: Naranjo, S.E., Castle, S.J. 2010. Sequential sampling plans for estimating density of glassy-winged sharpshooter, homalodisca vitripennis (Hemiptera: Cicadellidae) on citrus. Crop Protection Journal.29:1363-1370. Interpretive Summary: The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), invaded California in the early 1990’s. It poses a serious threat to grapes and other crop and ornamental plants mainly through its role as a vector of the bacterium Xylella fastidiosa Wells. In grapes it is called Pierce’s Disease and is fatal to the plant. Citrus is a favored host of GWSS and populations can be found in orchards year-round. Evidence suggest that citrus is a reservoir of GWSS that eventually invade grape fields. This study was conducted to develop an efficient sampling plan for estimating the density of nymphal and adult stages of GWSS in citrus orchards. Such a plan would aid researchers studying the population dynamics of this pest as well as provide a method to better study insecticide efficacy and perhaps even provide a means for deciding if pest control is necessary. From studies on the distribution of GWW on orange tree we determined that adults and nymphs were most abundant on the upper strata of the tree. Sequential sampling plans were then developed and validated based on samples drawn from the upper strata with a pole-bucket sampling device. Average sampling costs varied from about 21 to 189 minutes for a desired sampling precision of 25% depending on insect density and whether the goal is to sample nymphs, adults or both stages combined. These sampling plans developed on orange trees were robust, being equally effective for use on orange and lemon trees and on trees treated or not with insecticides.
Technical Abstract: The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is a serious pest of grapes and other crop and ornamental plants mainly through its role as a vector of the bacterium Xylella fastidiosa. Citrus harbors large populations of GWSS throughout much of the year in areas where the pest is problematic and improved understanding of the population dynamics and management of GWSS on citrus may be key to its management in the agricultural landscape. Study of population dynamics and the development of management strategies require effective and efficient sampling methods. Within-tree sampling distribution studies revealed that adults and nymphs are more abundant and less variable in the upper strata of citrus trees (>1.5 m). We developed and validated several fixed-precision sequential sampling plans for estimating the density of GWSS nymphs and adults using a beat bucket sampling method. Based on validation from resampling of independent data sets, Green’s sequential sampling model provided the best performance in estimating mean density with levels of precision equal to or better than the desired precision over a range of insect densities. Average sampling costs varied from about 21 to 189 minutes for a desired precision of 0.25 depending on insect density and whether the goal is to sample nymphs, adults or both stages combined. Further, the sampling plans developed on orange trees were robust, being equally effective on orange and lemon trees and on trees treated or not with insecticides.