SPATIAL PATTERNS OF AND SAMPLING METHODS FOR WESTERN FLOWER THRIPS (THYSANOPTERA: THRIPIDAE) ON GREENHOUSE SWEET PEPPER

Abstract

Intra- and inter-plant spatial patterns were determined for adult and immature western flower thrips, Frankliniella occidentalis (Pergande), on greenhouse sweet pepper at two commercial greenhouses using five sampling methods. The population density of the thrips was monitored biweekly for 4 months from May to August using blue sticky-traps, plant tappings, blossoms, plant leaves, and whole plants. The intra-plant spatial patterns of adult and immature populations of F. occidentalis were aggregated with the majority of the thrips collected from the top one-third of the plant. The inter-plant spatial patterns also were aggregated. The aggregation cluster for the adult thrips was at least three plants in size, although it was surmised to be at the individual plant level for immature F. occidentalis. The accuracy of the blue sticky-trap, plant tapping, blossom, and leaf samples was determined for monitoring the population densities of adult and immature thrips throughout the growing season. It was shown that leaves should be sampled from the middle section of the sweet pepper plant when using this sampling method. A precision-level sampling program was proposed for monitoring adult F. occidentalis on greenhouse sweet pepper. Sampling blossoms was the most cost-effective sampling method based upon time and number of samples for a specific precision level.