Pear Sawfly
(Pear Slug)

Family – Tenthredinidae

The pear sawfly, also commonly known as the pear slug, was common in Massachusetts in 1796. It was first recorded in Europe in 1740.

Life Stages
Egg: The egg is oval in outline, sometimes slightly flattened at one side, and measures 0.9 by 0.5 mm. It is pale green through the leaf tissue.

Larva: when first hatched, the larva measures 1.2 mm long and 0.5 mm wide at the thorax – the broadcast portion. The body is pale and free from slime; the head is light brown. As soon as the small slug begins to eat, the particles of green leaf tissue show through its body. The slug secretes a coat of slime soon after hatching and them appears dark olive-green, with a dark brown head. The slugs grow very rapidly at first. As the slugs grow, they become lighter colored. They are orange-yellow when fully mature.

Pupa: The pupa is 5.8 mm long, 2.4 mm wide and lemon yellow.

Adult: The adult is a sawfly. It is black and yellow, about 5 mm long – a little larger than the common housefly – and it has four wings.

Host Range
The pear sawfly is a pest of cherry, pear and plum. It is generally found in all pear-growing regions in Canada and the United States.

Injury or Damage
The larvae feed on the surface of the leaves and skeletonize them, leaving only a framework of veins.

Life History
The pear sawfly passes the winter in a cocoon formed in an earthen cell 2 or 3 inches below the surface of the ground. In the late spring, shortly after the cherries have come into full leaf, the adults emerge from these cocoons. After mating, the female inserts her eggs in the leaves. The eggs hatch in seven to 11 days. The young larvae emerge from the eggs to the upper surface of the leaf and cut semicircular holes in the epidermis. The young slugs begin toe at out small pieces of the leaf, first taking only the epidermis in patches, later eating deeper in large areas into the parenchyma to the veins. The feeding period varies from two to three weeks. They them crawl or drop to the ground, burrow into it and change to the pupal stage.

Adults emerge during late July and August and lay eggs for the second generation of slugs. This generation usually causes the greater amount of injury, especially on young trees, which they may completely defoliate. When this second generation of larvae becomes fully grown, they go into the ground and remain as larvae until the following spring, when they pupate.

Monitoring
In spring, shortly after pears or cherries have come into full leaf, examine leaves for olive-green, slug like larvae covered with slime that are eating out small pieces of the leaf. Re-inspect in late July or August for the summer generation.

Control
No special sprays are needed – the cover sprays applied for the common pests of pears will control it.