Garden sawfly

Systematic position: The garden sawfly (Messa hortulana) is a member of the order Hymenoptera and the family Tenthredinidae. These insects are known for their specific interaction with host plants, functioning primarily as leaf miners during their larval stages.

Host plants: This pest primarily targets trees within the Aceraceae family. Acer platanoides (Norway maple) and Acer campestre (field maple) are the most common hosts. When the population is dense, the damage becomes widespread, affecting the overall aesthetic and structural integrity of the trees.

Biology and lifecycle: Messa hortulana undergoes complete metamorphosis. Adults emerge in spring to mate and lay eggs within the leaf tissue. Larvae hatch and begin feeding inside the leaf, creating distinct mines. After reaching maturity, the larvae drop to the soil, where they construct cocoons to overwinter and pupate, preparing for the next generation cycle.

Nature of damage: As larvae, they are leaf miners. They consume the internal tissues of the leaves, leaving the upper and lower epidermis intact. These mines appear as irregular brown or translucent blotches on the foliage. Heavy infestation causes premature leaf senescence and shedding, which hinders the tree's ability to undergo photosynthesis effectively.

Control measures: Management of Messa hortulana involves several integrated approaches:

• Clearing and disposing of infested leaf litter during autumn to remove larvae.
• Cultivating the soil around the base of the trees to disturb cocoons.
• Applying systemic insecticides specifically timed with the adult emergence phase.
• Encouraging natural predators and parasitoids in the garden ecosystem to maintain balance.