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The grazing activities slug-like larvae of the pear and cherry slugworm sawfly can cause some leaves on pears, cherries, hawthorn, plum, Cotoneaster, Chaenomeles and Sorbus to dry up and turn brown.
Pear and cherry slugworm (Caliroa cerasi) on pear
Pear and cherry slugworms are the larvae of a sawfly. Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). The adult pear and cherry slugworm have black bodies about 4-6mm long and two pairs of transparent wings. Eggs are laid on the foliage and they hatch into larvae that are black with a slimy slug-like appearance. The larvae grow to a length of about 10mm and are somewhat club-shaped with the head end being swollen. When fully fed the larvae go into the soil to pupate.
There are two or sometimes three generations a year between June and October. The second generation in July and August can be the most obvious. Larvae that complete their feeding late in the year overwinter in cocoons in the soil before pupating in April to May of the following year.
The larvae feed by grazing away the upper surfaces of the leaves and the remaining portions of the grazed areas dry up and turn brown.
This insect can be tolerated. Heavy infestations can affect the appearance of the trees but the long term heath and on fruit trees the crop, is usually unaffected.
Regularly check the plant from June onwards for slugworm larvae and if feasible pick them off by hand.
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