Arrowhead scale

The arrowhead scale (Unaspis yanonensis) is a serious insect pest belonging to the order Hemiptera and the family Diaspididae. Originally native to East Asia, it has become a globally recognized quarantine pest due to its devastating impact on commercial citrus production in various climatic zones.

The primary hosts for this pest are citrus species, including mandarins, lemons, and oranges. The scale insect infestations typically occur on leaves, twigs, fruits, and bark. A heavy infestation can lead to significant tree stress, canopy thinning, and in severe cases, the death of branches or entire trees.

The biology of the arrowhead scale is complex, involving distinct stages: egg, crawler, and adult. The female scale is brown and oyster-shaped, while the male scale is small, white, and elongated. Depending on local temperatures, the insect may complete several generations per year, leading to rapid population explosions.

Damage is caused by the insertion of stylets into plant tissue to extract sap. This feeding process results in chlorotic spots on leaves and fruits. Because the scale covers the fruit surface, it renders the product unmarketable, causing severe economic losses for growers in infested regions.

Effective management requires an integrated pest management (IPM) strategy. Chemical control is most effective when applied during the crawler emergence phase, as the crawler stage lacks the protective hard scale covering. Furthermore, the introduction of parasitoid wasps has proven to be a successful long-term biological control method.

• Regular orchard scouting to determine crawler emergence timing.
• Application of systematic insecticides during the peak activity period.
• Biological control using Aphytis yanonensis wasps.
• Strict quarantine regulations to prevent spread to new citrus areas.