Apple sawfly

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.

Internal damage caused by apple sawfly larvae.

Quick facts

Common name Apple sawfly
Latin name Hoplocampa testudinea
Plants affected Apple fruits
Main symptoms Maggot holes in fruitlets that fall from the tree in early summer; elongate ribbon scars on mature fruits
Caused by Caterpillar-like larvae of a sawfly
Timing Late April-June

What is apple sawfly?

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.

Symptoms

Signs of an apple sawfly problem include:

  • In late May and June, damaged fruitlets have obvious holes with the larva’s blackish-brown excrement pellets spilling out
  • Each larva can damage several fruit
  • Affected fruitlets usually drop off the tree as part of the June drop (when apple trees shed excess fruits)
  • Fruitlets that suffered only initial feeding damage by a larva can stay on the tree and develop as fruits. These fruits are usually misshapen and have a long ribbon-like scar about 4mm wide, often starting at the eye end of the fruit and extending around the circumference. The fruit is usually still edible when this occurs

Control

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.

Non-chemical control

Pick off damaged fruitlets when they are seen to prevent the larvae moving to other fruitlets or going into the soil to pupate.

Chemical control

  • If damage has been heavy in previous years, a spray within seven days of petal fall with the contact pyrethroid insecticides deltamethrin (e.g. Provado Ultimate Fruit & Vegetable Bug Killer) or lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) may control the newly hatched larvae.
  • Manufactures instructions for pesticides on maximum dose, number of applications and harvest interval must be followed for food crops
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

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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