Hyacinth bulbs are propagated by hollowing them out or by making deep cuts. The bulbs treated in this way are stored in a special room (“hollowing room”) and they produce daughter bulbs. The bulbs in this room can be infected byThrips tabaci Lind., penetrating into the room from outdoors. Bulbs infected at an early date by this thrips produce no or only a few daughter bulbs. If infection takes place when daughter bulbs have already developed, then these young bulbs may rot away after planting.