Entomologia Experimentalis et Applicata 100: 235–243, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. 235 Unbiased estimation of greenhouse whitefly, Trialeurodes vaporariorum, mean density using yellow sticky trap in cherry tomato greenhouses Jong-Kwan Kim 1 , Jung-Joon Park 1 , Heungsun Park 2 & Kijong Cho 1,∗ 1 Department of Agricultural Biology, Korea University, 1-5 ka, Anam-dong, Sungbuk-ku, Seoul 136-701, Ko- rea; 2 Department of Statistics, Hankuk University of Foreign Studies, Yongin 449-791, Korea; ∗ Author for correspondence (Phone: 82-2-3290-3064; Fax: 82-2-925-1970; E-mail: kjcho@korea.ac.kr) Accepted: May 22, 2001 Key words: greenhouse whitefly, cherry tomato, enumerative sampling, yellow sticky trap, autocorrelation, Moran’s I, Homoptera, Aleyrodidae Abstract The spatial distribution of the count of adult greenhouse whiteflies, Trialeurodes vaporariorum (Westwood), on yellow sticky traps was analyzed using Taylor’s power law and spatial autocorrelation statistics in the cherry tomato greenhouses from 1998–1999. Samples were collected weekly using a cylindrically shaped yellow sticky trap placed in a 5 by 8 grid covering 0.10–0.15 ha in each of five cherry tomato greenhouses. Taylor’s (1961) power law indicated that counts of T. vaporariorum on traps were aggregated within greenhouses. Spatial auto- correlation analysis showed that trap catches were similar (positively autocorrelated) to a distance of 12.5 m, and then dissimilar (negatively autocorrelated) at >12.5 m. Autocorrelation-lag plots showed a globally significant spatial relation in 34 of 57 sample-weeks according to Bonferroni’s approximation. The presence of this spatial relation was not related to the changes of mean density. Trap counts at the second lag distance (12.5–25 m) showed little spatial autocorrelation and tended to be the most spatially independent. A fixed-precision-level sequential sampling plan was developed using the parameters from Taylor’s power law. The presence of spatial dependency in data sets degraded the sampling plan’s precision relative to performance in data sets lacking significant spatial autocorrelation. Therefore, to obtain an unbiased mean density of T. vaporariorum per greenhouse, sticky traps should be placed at least >12.5 m apart to ensure that they are spatially independent. Introduction The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), has expanded its distribution throughout Korea since its first detection in 1974 (Choe & Park, 1983). Now it is regarded as one of the most serious pests of the greenhouse cherry tomato, Lycopersicon esculentum Alef, due, in part, to a lack of effective control measures in Korea (Park et al., 1998). Chem- ical control of T. vaporariorum is difficult because pesticide resistant strains develop in most production greenhouses (Sanderson & Roush, 1992). Today, most growers in Korea prevent T. vaporariorum damage by applying up to 15 insecticidal sprays, generally as a tank mix with several fungicides. Worldwide, a successful biological control of T. vaporariorum has been achieved with the parasitoid Encarsia formosa (Gahan) when given proper environmental conditions (van Lenteren & Woets, 1988). However, biological control of T. vaporariorum in tomato greenhouses in Korea is still in its infancy, and there is a lack of research on precise recommendations concerning the use of E. formosa in commercial vegetable green- houses. Moreover, pesticide application for control of Tetranychus urticae Koch and Liriomyza trifolii (Burgess) disrupts biological control of T. vaporari- orum due to the low chemical tolerance of E. formosa (Johnson & Tabashnik, 1999). The development and implementation of pest man- agement strategies to control this insect depend on reliable and efficient monitoring tools for detecting and estimating pest density. The yellow sticky trap