Pear stem sawfly

The pear stem sawfly (Janus compressus) is a pest belonging to the order Hymenoptera and the family Cephidae. It is a specialized insect known for causing significant damage to young shoots of pear trees, making it a subject of concern for both commercial fruit growers and private gardeners.

The primary host for this pest is the pear tree (Pyrus). While it may occasionally be found on other members of the Rosaceae family, the pear tree remains its main target. The infestation can lead to stunted growth, loss of fruit-bearing wood, and overall weakening of the tree's vigor over several seasons.

The life cycle of the pear stem sawfly involves overwintering as mature larvae within silk cocoons in the soil. In the spring, the larvae pupate and emerge as adults. The females then locate young, succulent shoots to lay their eggs. A diagnostic behavior of the female is the circular incision made around the shoot, which serves to weaken the plant tissue for egg deposition.

Damage caused by Janus compressus is characterized by the wilting, yellowing, and eventual curling of the terminal shoots. Once the eggs hatch, the larvae bore into the stem, feeding on the pith and creating internal tunnels. This feeding activity disrupts the vascular system, leading to the death of the shoot tip and inhibiting the tree's ability to develop healthy new branches.

Management strategies focus on a combination of cultural and chemical control measures. Regular scouting during the spring is crucial to identify early signs of wilting. Prompt pruning and disposal of affected shoots, carried out before the larvae exit the stems to enter the soil, can significantly reduce the local population. In cases of high infestation, targeted insecticide applications during the adult flight period are recommended to break the life cycle.