Poplar spiral gall aphid

Systematic position: The poplar spiral gall aphid (Pemphigus spirothecae) belongs to the order Hemiptera and the family Aphididae. It is a highly specialized insect that exhibits a unique parasitic relationship with trees of the genus Populus, specifically acting as a gall-forming pest.

Host plants: The primary host for this species is the black poplar (Populus nigra). The aphid specifically targets the leaf petioles to create galls, which serve as an enclosed environment for colony development and protection from predators.

Biology and life cycle: The life cycle involves alternation between the primary poplar host and herbaceous roots. In the spring, the fundatrix (founder aphid) settles on the petiole, triggering hormonal changes in the plant tissue that cause the petiole to twist and swell into a spiral-shaped gall. The colony grows within this structure throughout the summer before migrating to alternative hosts.

Damage and economic impact: The presence of the aphid is identified by the prominent, twisted galls found on the leaf stems. High infestation levels can cause premature leaf drop, reduced photosynthetic efficiency, and significant aesthetic damage to ornamental poplar trees in urban landscapes or shelterbelts.

Protection measures: Management of Pemphigus spirothecae includes several key strategies:

• Sanitary measures, such as the removal and destruction of fallen leaves in autumn to disrupt the pest's overwintering cycle.
• Timing of chemical applications to coincide with the period before the galls have fully formed and hardened.
• Encouraging biological control agents, such as specialized predators and parasitoids that can penetrate galls.
• Site selection and planting of resistant poplar cultivars to mitigate the impact of the pest in high-risk areas.