Willow leaf-stalk gall sawfly

Systematic position: Pontania pedunculi is a species of sawfly belonging to the order Hymenoptera and the family Tenthredinidae. This insect is widely recognized for its unique ability to manipulate plant growth hormones to create specialized structures known as galls on willow species.

Host plants: The pest primarily infests various willow species (Salix spp.), including the goat willow (Salix caprea) and the eared willow (Salix aurita). These sawflies are often found in nurseries, urban parks, and natural riparian habitats where willows are common.

Biology and lifecycle: The lifecycle typically involves overwintering as larvae within cocoons in the soil or leaf litter. In the spring, the adults emerge to mate. The female uses her ovipositor to insert eggs into the leaf petioles or the base of the leaf blade. The irritation caused by the egg-laying and the subsequent feeding of the larva induces the plant to grow a gall around the insect.

Damage and pest impact: The damage is characterized by the presence of round or elongated, often reddish galls located on the leaf stalks. These galls divert nutrients away from the rest of the leaf, which can lead to localized necrosis, premature yellowing, and leaf drop. While healthy mature trees often tolerate light infestations, severe outbreaks can impact the growth and vigor of young trees.

Control measures: Management strategies for Pontania pedunculi include:

• Sanitation, which involves raking and destroying fallen leaves in autumn to remove the overwintering population.
• Application of systemic insecticides at the very beginning of the spring flight period when females are laying eggs.
• Biological control by encouraging predatory insects and birds that feed on sawfly larvae.