Lebanese wheat stem sawfly

The Lebanese wheat stem sawfly (Trachelus libanensis) belongs to the order Hymenoptera and the family Cephidae. Adult insects are slender, measuring 8–10 mm in length, typically with black bodies and occasional yellow rings on the abdomen.

Females are equipped with a specialized ovipositor, which they use to slit plant stems and deposit eggs inside. Larvae have an S-shaped, yellowish-white body and feed on the internal tissues of cereal stems as they develop.

The species is univoltine, completing only one generation per year. Larvae overwinter within the stubble of cereal crops, pupating inside the lower part of the stem once spring temperatures rise.

Adult emergence typically coincides with the booting or heading stages of cereal crops. Environmental conditions, specifically humidity and temperature, play a crucial role in the timing of their activity.

Correct identification often involves inspecting the base of the stems for larval galleries. Laboratory examination may be necessary to distinguish this species from other related stem sawflies.

The primary hosts for this pest include wheat (winter and spring varieties), barley, and rye. It may also utilize wild grass species as alternative hosts if the primary crop is unavailable.

Larval feeding causes the most significant damage. By boring through the internal structure of the stem, the larvae disrupt the nutrient flow to the head of the wheat plant.

This disruption prevents the grain from filling properly, resulting in shriveled kernels, reduced test weight, and lower overall quality of the harvested produce.

High infestation levels can significantly reduce seed viability and energy, causing economic losses for farmers due to both lower yield and reduced grain marketability.

The weakened stem structure makes the crop highly susceptible to lodging, especially during windy or rainy weather, which severely complicates the mechanical harvesting process.

Initial signs of infestation appear as small slits or puncture marks on the lower sections of the stem where eggs were laid. These can be detected during scouting in the spring.

As larvae develop, the plants often exhibit signs of premature ripening, with the heads becoming noticeably pale, a condition sometimes referred to as whiteheads.

A key indicator is the increased fragility of the stems near the base. The stems become brittle and break easily upon mechanical stress or strong winds.

Dissecting a stem reveals internal tunnels filled with larval frass, which serves as a definitive sign of active infestation by stem sawfly larvae.

Scouting after harvest is also vital, as finding hibernating larvae within the crop stubble indicates a high likelihood of continued pressure in the following season.

Deep tillage or plowing of the soil after harvest is highly effective, as it destroys the stubble where larvae overwinter, preventing the next generation from emerging.

Crop rotation remains a fundamental practice, as diversifying crops reduces the build-up of sawfly populations by breaking the life cycle of the pest.

Growing resistant varieties with thicker stem walls provides a physical barrier, making it more difficult for larvae to survive and thrive within the plant structure.

Chemical control can be implemented during the adult flight period, using systemic insecticides if thresholds for economic damage are reached.

• Stubble cultivation immediately after the grain harvest.
• Control of volunteer cereals and grassy weeds in the fields.
• Timely harvesting of the crop to minimize losses due to stem breakage.