Alder leafhopper

The alder leafhopper (Alnetoidia alneti) is an insect species belonging to the order Hemiptera and the family Cicadellidae. It is a common sap-feeding pest primarily associated with alder trees. Adults are slender, pale green or yellow-green insects, typically found on the undersides of leaves.

While the insect is host-specific to alder (Alnus spp.), it can occasionally be found on related trees such as birch (Betula) and hazel (Corylus). The pest thrives in temperate regions, often becoming a significant issue in nurseries, public parks, and forest fringes where the microclimate is favorable for its rapid reproduction.

The life cycle of Alnetoidia alneti generally consists of one or two generations per year. They overwinter as eggs, which are inserted into the bark of twigs or near the buds. As soon as temperatures rise and buds burst, the nymphs emerge and start feeding immediately. They go through several nymphal instars before reaching the adult stage.

Damage is characterized by stippling, where the feeding action causes small white or yellowish dots to appear on the upper surface of the leaves. As the infestation intensity increases, these spots coalesce, leading to general leaf chlorosis and premature leaf drop. This reduces the tree's photosynthetic capacity, stunting its overall growth and vigor.

Effective management strategies for controlling the alder leafhopper include:

• Monitoring foliage for early signs of stippling during late spring.
• Applying systemic insecticides if the infestation threshold is exceeded.
• Promoting biodiversity to encourage natural predators like ladybugs, lacewings, and spiders.
• Maintaining healthy soil moisture to prevent drought stress, which makes trees more susceptible to infestation.