Ussurian oyster shell scale

The Ussurian oyster shell scale (Lepidosaphes ussuriensis) is a destructive insect pest belonging to the order Hemiptera and the family Diaspididae. It is a well-known pest in temperate regions, frequently infesting ornamental and fruit-bearing trees, often causing significant damage if left unmanaged.

This insect primarily infests deciduous trees and shrubs. Common host plants include species from the Rosaceae family such as apple and pear trees, as well as maple and linden trees. The scale insects settle on the bark of twigs, branches, and trunks, forming dense colonies that are difficult to notice in the early stages of infestation.

The biology of this pest involves one generation per year. Fertilized females overwinter under their protective shields on the bark. In late spring, as temperatures rise, females lay eggs. Once the eggs hatch, the nymphs, known as crawlers, move actively across the bark to find suitable feeding sites, which is the primary period for dispersal.

The damage caused by the Ussurian oyster shell scale results from the insect sucking sap from the phloem, which drains the tree's energy. Heavy infestations cause the bark to crack, hinder the growth of young shoots, and lead to the dieback of branches. Over time, weakened trees become susceptible to secondary infections and environmental stress.

Management strategies include a combination of mechanical and chemical approaches.

• Pruning and removing heavily infested branches.
• Applying horticultural oils in the dormant season to smother overwintering females.
• Timing insecticide applications to coincide with the crawler stage, when the insects are most vulnerable.
• Maintaining tree vigor through proper fertilization and irrigation.

A proactive monitoring program is essential to prevent large-scale outbreaks in orchards. Regular inspection of bark surfaces, particularly on younger, susceptible trees, allows for early intervention, which significantly reduces the need for heavy pesticide usage later in the growing season.