Dispersal of adult western flower thrips (Thysanoptera: Thripidae) in greenhouse crops

Abstract

AbstractThis study characterized the spatial distribution of adult western flower thrips,Frankliniella occidentalis(Pergande) (Thysanoptera: Thripidae), released at the centres of greenhouses stocked with either cucumber (Cucumis sativusL. (Cucurbitaceae)) or chrysanthemum (Dendranthema grandiflora(Tzelev) (Asteraceae)) plants. Experiments conducted using either adults marked with fluorescent powder or unmarked adults revealed that the density of females per plant decreased as an inverse function of the distance from the release point. Inverse regression models with steep decreases in density over small distances may commonly describe the dispersal behaviour of insects that have limited flight capacity and settle on the first plants that they encounter. Females were found on plants farther from the release point as time elapsed, dispersing throughout the greenhouse at an average rate of 0.18 to 0.29 m per day. Distinct sex ratios for adults captured on sticky cards or sampled on host plants suggested that males and females exhibit different dispersal behaviours. The spatial distribution ofF. occidentalisvaried across generations, with females exhibiting a lower level of aggregation around the release site than their nymphal progeny. The average rate of spread between consecutive generations fluctuated between 0.05 and 0.17 m per day. Considering the limited dispersal ofF. occidentalis, outbreaks may be effectively suppressed by applying insecticides or releasing natural enemies in relatively small concentric areas surrounding heavily infested plants, as well as near the edges of greenhouses.