Seasonal prevalence of the occurrence of western flower thrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) on weed hosts growing around ornamental fields

Eighteen weed species were surveyed for western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), from spring through autumn in 1994 within an ornamental production area in central Japan. WFT were collected from eight weed species and occurred as the predominant thrips species on most of the weed species in April. In early April, the densities of WFT adults and thrips larvae were high on racemes of common groundsel. From April to May, the densities of WFT on flowers of narrowleaf vetch, dandelion, and white clover increased rapidly Between June and July, WFT adults inhabited predominately the Poaceae weed, but the density of their larvae was low. Furthermore, WFT became the minor colonizers on several weed species from August onward. These results suggest that WFT inhabit and reproduce predominately on numerous weed species flowering around the fields in spring, so the removal of weeds flowering in early spring is important for the control strategy of WFT.