When apple trees are in flower, the sawfly, Hoplocampa testudinea, lays its eggs in the developing fruit. In June, the larvae tunnel their way under the skin of the fruit and into the core, causing the apples to fall. When they’re ready, they tunnel out of the apples, creating a second hole, and then bury themselves in the soil to pupate. Sometimes the larvae die and don’t make it to the middle of the apple, in which case the apples mature, but they’ll have ribbon scars and are sometimes misshapen.
The larvae of the sawfly damage the apples, either causing fruitlets to fall in June, or those that are left on the tree gradually become ribbon-scarred and are sometimes misshapen.
Find it on
Closely examine young fruits on the tree or on the ground, and destroy any that show signs of entrance holes. This stops the larvae from escaping into the soil and pupating. Rake the soil around affected trees in winter, so the exposed sawflies are killed by frost.