European apple sawfly

Description. Eggs are 0.8 mm long, shiny, oval and transparent. Newly hatched larvae measure about 1.7 mm in length and are light cream coloured with a black head and caudal (rear) shield. By the time larvae reach the mature fifth instar, they are 9-11 mm long, and their head and shield have become pale brown in colour. There are five larval instars. The adult is 7-8 mm long with light orange to yellow head, antennae, lower body and legs - the upper body is dark brown and shiny. The female is slightly larger than the male.
Biology. European apple sawfly overwinters as a mature larva in a cocoon a few centimetres below the soil surface. The larva pupates in the spring and adults emerge during the pink stage of apples. The female European apple sawfly lays eggs just after the king flower opens. Eggs are deposited singly at the calyx end of the flower, often at the base of or between the stamens. After 8-10 days, newly hatched larva burrow into the apple and feed on tissue just below the skin. As the larva matures, it tunnels deeper into the seed cavity and feeds on one or two seeds. Larva often move between developing fruitlets. Larva matures in four to six weeks, then leave the fruit (which has usually dropped), burrow into the soil and form a cocoon in preparation for pupation. There is one generation per year. Diapause may last for up to three years.
Damage. First instar larvae feed beneath the fruit skin and create a heavily russeted, winding, ribbon-like scar that spirals out from the calyx end. If larva ceases feeding at this early stage, for whatever reason, this damage will likely be seen on mature fruit at harvest. If this tunneling stops early, tunneling scars are short and indistinguishable from damage caused by the tarnished plant bug. 
Second instar larvae tunnel into fruit towards the seed cavity. Reddish-brown frass is often seen protruding from an exit hole in fruit. Larval feeding into the core of the apple often causes fruit to abort, while sub-surface feeding creates scars visible on the fruit at harvest.
As the larva molts and matures, it moves towards the seed cavity or adjacent fruit. As the larva feeds internally, it enlarges its exit hole with wet, reddish-brown frass on the side of the fruit. The larva moves to other fruit in the cluster to continue feeding. A single larva can damage several apples. Damaged fruit drops during the "June drop" period. In insecticide-free apple orchards in Quebec, approximately 4% of the apple crop in affected orchards can be damaged by European apple sawfly.
Injury from secondary feeding causes fruit to drop. Secondary injury by European apple sawfly can be confused with codling moth damage. There are three ways to distinguish these two pests.
1. Damage from European apple sawfly usually appears before codling moth damage occurs. European apple sawfly damage appears in orchards two to three weeks after petal fall - coding moth larvae and damage appear five or more weeks after petal fall.
2. The smell of the frass of European apple sawfly is strong - codling moth frass is odourless.
3. European apple sawfly larva is yellowish white and has seven abdominal legs. Codling moth larva is larger than European apple sawfly larvae, pinkish-white in colour and has five abdominal legs.