Ash sawfly

The ash sawfly Tomostethus melanopygius is a species of insect belonging to the order Hymenoptera and the family Tenthredinidae. It is recognized as a specific defoliator of trees within the genus Fraxinus, playing a significant role in the health of ash-dominated forest ecosystems and urban landscapes.

The host plant for this pest is exclusively the ash tree. The larvae feed on the foliage, and when populations reach high densities, they can cause severe defoliation across large areas. This loss of canopy cover weakens the trees, making them susceptible to secondary pests, wood-boring insects, and various fungal diseases.

The life cycle of Tomostethus melanopygius is univoltine, meaning there is one generation per year. Adult sawflies emerge in the spring to coincide with the opening of ash buds. Eggs are deposited into the leaf tissue, and the subsequent larval stage feeds voraciously until late spring or early summer before entering the soil to pupate and overwinter.

The damage caused by the larvae is characterized by skeletonization and total consumption of the leaves. As the larvae mature, they consume larger portions of the leaf blade, leaving only the primary veins. Significant defoliation events negatively affect the tree's photosynthesis capacity, leading to stunted annual growth and reduced overall vigor.

Effective management and protection strategies for the ash sawfly include:

• Application of targeted insecticides during the early larval development stage.
• Cultural practices such as tilling the soil beneath infested trees in autumn to disrupt pupal overwintering.
• Encouraging biological control agents, such as parasitic wasps and predatory birds, that feed on sawfly larvae.
• Regular forest health monitoring to detect early signs of infestation and prevent large-scale outbreaks.