Forbes Scale: Appearance, Territory, Damage and Life

Latin name: Quadraspidiotus forbesi

Appearances: They resemble fish scales on the plant because they are small, motionless, and lack any apparent legs or antennae. Living young (crawlers) are born from female scales under the edge of the scale covering. Although they are bigger and brown in color, late crawler stages resemble San Jose scale. Adults resemble San Jose scales as well, with the exception that Forbes scales have a raised, reddish region in the middle as opposed to San Jose’s center having a pale-yellow nipple.

Host plant: Fruit trees such apple, cherry, peach, apricot, pear, plum, and others are the most typical hosts.

Territory: Eastern North American states and provinces that grow the majority of fruits.

Damage insect caused: Attacks quince, cherry, apple, apricot, pear, and cherry. The bark of the trunk and branches is covered with profusions of grey, thin, flaky scales, sometimes entirely. Crawlers move toward fruits, where their feeding results in tiny red spots with a light-colored region in the center that are roughly 3 mm in diameter. Like San Jose scales, Forbes scales also inflict damage by sucking sap from twigs, branches, and fruit. They may also inject salivary toxins while sucking. Trees may eventually deteriorate and pass away.

Life cycle and habits: The San Jose scale overwinters as immature scales on the tree. By the time tree sap begins to move in the spring, they are fully grown and latent on the bark by late May. Males that are actively looking for females to mate with emerge from their scales. Females are immobile and live their entire lives covered in scales. Females start to produce live young after mating, often at a rate of 9–10 per day. They give birth to 150–500 children after six weeks of reproduction (crawlers). Crawlers crawl to find an appropriate location to develop (bark or fruit), after which they pierce the bark with their mouthpart to start feeding on sap. They molt and shed their skin three weeks later. Their sucking mouthparts hold the scales to the bark. As the insects develop, they surround themselves with a waxy coating that shields them from insecticides, desiccation, and predators. Males go through four nymphal instars to reach adulthood, compared to two instars for females. In hot, dry conditions, scale populations grow quickly, and females give birth to more than 300 million young annually. Every year, there are two whole generations.