Suppressive effect of red light irradiation on attractiveness of Thrips palmi Karny (Thysanoptera: Thripidae)

We tested the effect of red and white light irradiation of cucumber seedlings on the movement of melon thrips ( Thrips palmi Karny 1925) over a 10-day period. Two cucumber seedlings were placed at opposite ends of a clear 99 × 39 × 43-cm acrylic box; one of the seedlings was irradiated with red and white light, and the other was irradiated with white light only. A seedling with approximately fifty adult thrips was then placed at the center of the box and the seedlings at the opposite ends of the acrylic box were monitored to determine which of the irradiated seedlings attracted more thrips. We performed four experiments in which the bottom surface materials and light wavelengths were changed. When the color of the bottom surface was not changed (i.e. remained a clear acrylic plate), the thrips significantly avoided the cucumber seedling that was irradiated with red and white light. When black drawing paper or aluminum foil were used to cover the bottom surface, a significant number of thrips avoided the cucumber seedling that was irradiated with red and white light. When aluminum foil was used to cover the bottom surface and the red and white light was changed to orange and white light, the thrips did not avoid the cucumber seedling that was irradiated with orange light. Thus, it appears that some bottom surface materials under red irradiation can have a marked suppressive effect on attractiveness of thrips.