The Japanese flower thrips, Thrips setosus, originates from Japan and Korea and was recently introduced into Europe. It was found in a Hydrangea nursery in the Netherlands in 2014 and has since then also been reported from several other European countries. Currently, it is a pest of greenhouse grown Hydrangea in the Netherlands and other European countries. In Japan, it has reportedly affected a wide range of host plants but not Hydrangea.
Life cycle and appearance of Japanese flower thrips
The Japanese flower thrips (Thrips setosus) develops in six stages: egg, two larval instars, prepupa, pupa, and finally the adult insect. The eggs of the Japanese flower thrips are laid into the plants tissue and pupation takes place in the ground. Adult females pass the winter in reproductive diapause.
Adult females are about 1.3mm long and have a pale basal quarter of the wings, which contrasts with the otherwise dark brown body and wing colour. The larvae and the adult males are yellowish. The prepupal and pupal instars can be recognized by their developing wing buds. They do not feed and only move if disturbed. In the adults, both pairs of wings are fully developed.
Despite its common name, the Japanese flower thrips is mainly a leaf-feeding thrips. However, in Hydrangea it also feeds on the flowers. Thrips cause damage to plants by piercing the cells of the surface tissues and sucking out their contents, causing the surrounding tissue to die. The resulting silver-grey patches on leaves and the black dots of their excreta indicate their presence in the crop. The vigour of the plant is reduced by loss of chlorophyll. When infestations become serious the leaves themselves can shrivel. In addition to the this direct damage, the Japanese flower thrips is also able to transmit tomato spotted wilt virus (TSWV).