Acanthaspidiotus borchsenii

Acanthaspidiotus borchsenii is a member of the Diaspididae family (armored scale insects), within the order Hemiptera. These insects are characterized by a tough, protective shield formed from their own secretions and larval exuviae.

Females are sedentary and wingless, remaining firmly attached to the host plant throughout their adult life. They possess a specialized stylet used to pierce plant tissues and extract nutrients.

Males, although winged and capable of flight, are rarely seen due to their short lifespan and lack of mouthparts. Their sole function is to locate and fertilize the sessile females.

Identification at the species level is complex and often requires professional microscopic examination of the pygidium, a structure located at the posterior end of the female's body.

Due to their small size and cryptic coloration, which blends with the bark of trees, these insects are often overlooked until the infestation becomes quite severe.

The pest primarily targets woody plants, shrubs, and ornamental trees. It is particularly concerning in nurseries, landscape design areas, and forest ecosystems where diverse tree species are grown.

By constantly extracting plant sap, the insect disrupts the physiological processes of the tree. The loss of nutrients leads to reduced vigor and stunted growth of the entire plant.

The extraction points on the bark become sites of localized tissue damage. This can lead to bark splitting, necrosis, and the entry of pathogens into the vascular system of the tree.

Heavy infestations result in a coating of scales over the twigs and branches. This blocks normal gas exchange through the lenticels of the bark and weakens the plant's structural integrity.

In severe cases, the cumulative damage leads to dieback of branches, premature leaf drop, and eventually the death of the entire plant if no control measures are applied.

The life cycle of Acanthaspidiotus borchsenii is heavily dependent on ambient temperatures. Winter is typically passed in a quiescent state, often as mated females or first-instar nymphs under their shields.

As temperatures rise in the spring, the metabolism of the scale increases, and the insects resume feeding. This coincides with the start of the sap flow in the host trees.

The reproductive phase occurs during the warmer summer months. Depending on the geographical region and cumulative heat units, the insect may complete one or more generations per year.

The mobile stage, known as the "crawler," is the primary time of dispersal. Crawlers emerge from under the mother's shield to find new, suitable feeding sites on the plant.

Autumn triggers a preparation for winter. The insects slow their activity and thicken their shields or find protected crevices to survive the cold temperatures until the following spring.

The most visible sign of an infestation is the presence of hard, bump-like scales on the bark of branches. These look like small, raised spots that feel rough to the touch.

Affected plants often show signs of general chlorosis (yellowing of leaves). This is a result of the plant being drained of essential resources needed for chlorophyll production.

Growth suppression is a common symptom. The annual shoot increment is significantly reduced, and the plant appears to be failing to thrive despite adequate water and nutrient supply.

In later stages, dieback of the crown or specific branches is observed. This is often accompanied by thinning of the foliage, making the canopy look sparse and unhealthy.

Close inspection of the underside of branches often reveals dense clusters of these scale insects, which can be scraped off with a fingernail, leaving a small mark on the bark.

Prevention starts with strict phytosanitary checks. Ensuring that all new nursery stock is free from scale insects is the most effective way to prevent the introduction of this pest.

Cultural control involves the judicious pruning and disposal of heavily infested limbs. This practice helps to decrease the local population density and slows down the spread.

Chemical control is most effective when timed with the emergence of the crawler stage. Systemic insecticides can be used to treat the plant, making the sap toxic to the feeding scales.

Biological control methods, including the release of predatory wasps or ladybirds that specialize in feeding on scale insects, are highly effective in stable, managed environments.

Regular monitoring of trees during the growing season allows for early detection. Timely intervention, especially during the crawler stage, significantly reduces the need for heavy pesticide applications.