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Apple sawfly larvae can damage apple fruits at the fruitlet stage in late spring to early summer, affected fruits usually drop off in June. This should not be confused with maggoty apples in late summer which are caused by the codling moth.
Internal damage caused by apple sawfly larvae.
Adult apple sawflies are small winged insects with blackish brown heads and thorax and brown abdomens. The caterpillar-like larvae initially tunnel beneath the skin of developing apples, causing a scarring, before burrowing into the fruit.
Signs of an apple sawfly problem include:
Apple sawfly is not such a widespread problem as codling moth, although some cultivars, such as ‘Worcester Pearmain’, ‘Charles Ross’, ‘James Grieve’ and ‘Ellison’s Orange’, seem to be particularly susceptible. Apart from ‘Early Victoria’ and ‘Edward VII’, cooking apples are rarely attacked and need not be treated against this insect. In years when there has been a heavy fruit set, a bit of fruit thinning caused by apple sawfly can be beneficial.
Pick off damaged fruitlets when they are seen to prevent the larvae moving to other fruitlets or going into the soil to pupate.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Adult apple sawflies are active in late April-May and can be seen visiting the open blossom. They are 4-5 mm long, the head and thorax are blackish brown and the abdomen is brown.
Eggs are laid at the base of the flowers. After petal fall, the eggs hatch and the caterpillar-like larvae start feeding. Initially the larvae tunnel beneath the skin of the developing fruitlets. Later they bore into the core of the fruitlets, and this feeding damage causes affected fruit to drop in early summer. If the larva dies before reaching the core, the fruit can survive and develops but has a ribbon-like scar on the skin where the early feeding took place.
When fully fed, the larva is about 10mm long and has a brown head and white body. Each larva can damage 3-5 fruitlets before it completes its feeding and goes into the soil, where it overwinters as a non-feeding larva and pupates in the following spring.
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