Robinia sawfly

The Robinia sawfly (scientific name Nematus tibialis) is a destructive insect species classified within the order Hymenoptera and the family Tenthredinidae. This pest is a specialist that primarily targets plants belonging to the genus Robinia, causing significant stress to both wild and cultivated populations.

The primary host for this sawfly is the black locust (Robinia pseudoacacia). When populations reach high densities, the sawfly can cause extensive defoliation of these trees. This feeding damage not only affects the aesthetic value of ornamental specimens but also hampers the growth rate and overall vitality of young trees in plantations.

The biological cycle of Nematus tibialis consists of several stages: egg, larval, pupal, and adult. The females oviposit into the leaf tissue of the host. Upon hatching, the larvae, which are caterpillar-like in appearance, feed voraciously on the foliage. Once their development is complete, they descend to the ground to pupate within a silken cocoon in the soil.

The damage caused by the larvae is characterized by the consumption of the leaf blades. In severe infestations, only the midribs and primary veins remain, a condition known as skeletonization. Such severe defoliation triggers a loss of photosynthetic capacity, potentially leading to branch dieback or total mortality of susceptible or weakened specimens.

Integrated Pest Management (IPM) is crucial for controlling Nematus tibialis. Monitoring is the first step, specifically watching for larval emergence in early spring. Chemical control using selective insecticides is highly effective when applied during the early larval stages, while biological controls, such as naturally occurring predators or microbial sprays, can be used in sensitive environments.

• Monitor for leaf damage or presence of larvae in spring.
• Encourage local bird populations that prey on sawfly larvae.
• Apply systemic or contact insecticides when infestation threshold is met.
• Implement mechanical removal in small-scale or ornamental settings.