Aggregation Indices and Sample Size Curves for Binomial Sampling of Flower-Inhabiting Frankliniella Species (Thysanoptera: Thripidae) on Tomato

Abstract

Western flower thrips, Frankliniella occidentalis (Pergande), females inhabit tomato flowers and insert eggs into developing fruit, causing cosmetic damage. The species is a vector for tomato spotted wilt virus. Only larval thrips acquire the disease, and larvae developing to adult on infected plants can disperse and infect additional plants in a field. Tobacco thrips, F. fusca (Hinds), another vector species, and flower thrips, F. tritici (Fitch), a nonvector species, also inhabit tomato flowers but apparently do not reproduce in the flowers. Our objectives were to determine dispersion characteristics of these thrips in tomato flowers and to determine relationships between density and incidence for developing a presence/absence sampling program. Taylor’s power law indices indicated that populations of F. occidentalis and F. tritici were aggregated. Larvae of F. occidentalis were more aggregated than adults. Populations of F. fusca were aggregated in 1988, but randomly dispersed in 1989. Aggregation indices were used to determine relationships between incidence and density and to develop sample size curves for use in a binomial sampling program. Adults of F. occidentalis and F. tritici were estimated using presence/absence sampling at densities <1.4 per flower; binomial sampling was reliable for F. fusca at densities <2.0 per flower. Sixteen to 18 flower samples were needed to estimate thrips densities at the 25% precision level.