Ash borer

The ash borer (Podosesia syringae) is a moth species belonging to the family Sesiidae, known commonly as clearwing moths. These insects are masters of mimicry, resembling wasps or hornets in both appearance and flight pattern, which serves as a potent defensive adaptation against avian predators.

This pest primarily infests trees in the Oleaceae family. While it is widely known as a threat to lilac (Syringa), it also frequently attacks species of ash (Fraxinus) and privet (Ligustrum). It is particularly detrimental in nursery settings, urban landscapes, and forest plantations where susceptible host trees are cultivated.

The biological cycle of this species is typically completed in one year. Mated females deposit their eggs on the bark of susceptible trees, often near pruning scars, cracks, or mechanical wounds. Upon hatching, the larvae bore into the inner bark and cambium layer. They overwinter as larvae within the woody tissue, where they continue feeding until pupation occurs in the spring, just before the adults emerge.

The damage caused by the ash borer is significant, as larvae create galleries beneath the bark that disrupt the tree's vascular system. Symptoms of infestation include reduced vigor, dieback of the crown, and the presence of frass (sawdust-like excrement) around entry holes. Severe or repeated infestations can lead to structural instability or death of the host tree.

Control and management strategies are vital for maintaining tree health and include:

• Maintaining tree vigor through proper watering and fertilization to help them resist boring insects.
• Careful pruning of infested branches and stems during the dormant season to remove larvae before emergence.
• Applying protective coatings or specialized horticultural treatments to pruning wounds.
• Using preventative insecticide sprays on the bark during the adult flight period to intercept eggs or young larvae before they enter the wood.