Fruit Tree Pest
Arrowhead Scale
Order: Hemiptera
Family: Diaspididae
▶Scientific name: Unaspis yanonensis (kuwana)
▶Common name: Arrowhead scale
▶Size: 2.5 ~ 3.5mm
▶Host plants: Citrus species such as tangerine, trifoliate orange, yuzu,
and other related plants
▶Distribution: Korea, Japan, China, Taiwan, and neighboring regions.
Adult females measure 2.5 - 3.5 mm and are enclosed in a dark brown, mussel-shaped shell. They infest branches, leaves, and fruits. Their prolific reproduction leads to high infestation density, which can cause twig dieback or even tree death. When adult females infest fruit, they appear like tiny sesame seeds, drastically reducing commercial value. The infested areas of fruit fail to color properly and often remain green, further lowering marketability.
They used to overwinter as adults. The first-generation first- instar nymphs emerge in mid-May. Female oviposition continues for about two months. The newly hatched crawlers move briefly before settling and becoming sessile. After passing through the second instar, the first generation of adults appears in early May, and the second-generation first instars emerge in late July. In some regions, a third generation appears in late September to October. The nymphs migrate to fruits mainly during the second or third generation.
