A sampling system for estimating population levels of the citrus thrips, Scirtothrips aurantii Faure (Thysanoptera: Thripidae), in mango orchards.
Grové T., Pringle K. L.
Author Affiliation: ARC - Institute for Tropical and Subtropical Crops, Private Bag X11208, Nelspruit, 1200, South Africa.
African Entomology 8 : 223-226
Abstract : Data were collected over a two-year period (1993/95) at four localities in Mpumalanga Province, South Africa, to formulate a sampling technique for monitoring population levels of the citrus thrips, Scirtothrips aurantii Faure, in mango orchards. Using a two-stage sampling system for determining population levels, the optimum combination of the number of trees per orchard (primary units) and fruit per tree (secondary units), was estimated. Taylor's power law regression of log (S2) on log (X?..) provided a good fit for both the within-tree (r2=0.887) and between-tree (r2=0.746) data. The value for the aggregation coefficient, b, in both cases was >1, indicating a clumped distribution. Sampling precision, D, improved with increasing average numbers of S. aurantii per fruit. In addition, keeping the total number of fruit examined constant, sampling precision at low population levels improved by increasing the number of trees sampled and decreasing the number of fruit examined per tree. Examining 50 fruit per orchard should be sufficient for obtaining suitably accurate population estimates for pest management purposes.