White apple scale

The white apple scale (Aulacaspis mali) is a destructive sap-sucking pest belonging to the order Hemiptera and the family Diaspididae. As a specialized phytophagous insect, it poses a significant threat to orchards by depleting the vitality of fruit trees through constant nutrient extraction from the vascular system.

This species primarily targets pome and stone fruit trees, including apple, pear, and various plum varieties. The pest is typically found on the bark of trunks, branches, and occasionally on shoots. Due to their small size and protective armor-like scales, they are often overlooked until a severe infestation has already caused visible physiological decline in the host tree.

The life cycle involves overwintering as fertilized adult females underneath their hardened protective scales. As temperatures rise in the spring, females commence egg-laying. The resulting crawlers are the only active mobile stage of the insect; they disperse across the plant surface before settling down permanently, losing their legs, and secreting a new protective cover as they mature.

Damage to the plant is systemic. As the insects feed, they inject saliva that can disrupt plant tissue, leading to bark cracking, stunted growth of twigs, and severe limb dieback. Heavy infestations lead to a reduced photosynthetic area, poor fruit set, and significant winter mortality of branches, eventually weakening the entire tree structure and making it susceptible to secondary pathogen attacks.

Effective control strategies require an integrated pest management approach. Recommended actions include:

• Cultural control: pruning out heavily infested limbs and scrubbing bark to reduce wintering sites.
• Dormant oil sprays: applying horticultural oils in early spring to smother the overwintering females.
• Insecticide applications: targeting the crawler stage, which is the most vulnerable point in the life cycle.
• Natural enemies: preserving populations of parasitic wasps and ladybird beetles that prey on scale insects.