Direct Feeding Damage on Cucumber by Mixed-Species Infestations of Thrips palmi and Frankliniella occidentalis (Thysanoptera: Thripidae)

Abstract

Distributions of Thrips palmi Karny and Frankliniella occidentalis (Pergande) within plants and relative contributions of each species to fruit scarring were investigated in field plantings of cucumber, Cucumis sativus (L.). Densities of T. palmi (number per unit area plant substrate) were greatest on foliage, whereas F. occidentalis densities were greatest on flowers. Densities of both species were lowest on fruits. Both species had secondary sex ratios that were biased towards females. The proportion of male F. occidentalis increased substantially in flower samples. Temporal variation in the incidence of fruit scarring, within and between field plantings, was related to variation in densities of F. occidentalis (but not T. palmi ). Within-field spatial variation in fruit scarring on a given harvest was also associated primarily with variation in F. occidentalis densities. Because small, developing fruits physically support the female flowers, the high densities of F. occidentalis in flowers may create opportunities for them to incidentally feed upon and scar young fruit.