Attack of the Leaf Curling Midge

Have you ever seen tightly curled leaves that are dry and crusty on your apple tree? If you open these leaves and look inside you will see several orange maggot like larvae feeding on the surface of the leaf. What are these weird and wonderful insects? They are the larvae of the apple leaf curling midge.

The adult apple leaf curling midge is a small fly approximately 1.5 to 2.5 mm in length. The adults mate, and females lay their eggs on apple leaves that are partially unfolded. The eggs hatch and the emerging larvae begin to feed on the apple leaves. The larvae are initially red coloured, however, they eventually turn bright orange in colour when fully mature. The larvae spend most of their lives in the rolled up leaf. Generally, a curled leaf contains 20 to 30 larvae, however, as many as 500 larvae can been found in an infested leaf. The margins of infested leaves are rolled in towards the mid-vein of the leaf. Larval feeding prevents the infested leaf from unfolding, and the leaf continues to become more tightly rolled as the leaf continues to grow.

Mature larvae exit the curled leaves and fall to the ground. After a heavy rainfall the larvae emerge from the leaves and move into the soil beneath infested trees. The insects pupate and the adults emerge. Apples are the only host of the leaf curling midge. Some varieties with lush terminal growth may be preferred due to the availability of egg laying sites, however, all cultivars are susceptible to infestation.

These insects are not considered to be an economic pest of apples, however, high insect populations in nurseries or in young trees may result in reduced photosynthesis, and may stunt the growth of terminal shoots. In the past this insect has likely been controlled by broad spectrum insecticides applied against key pests. However, these insects are becoming more prevalent in orchards as we move away from using broad spectrum insecticide programs.

It is very difficult to manage this pest using insecticides since the midges are well protected inside the curled-up leaves. Currently Matador (pyrethroid) is the only product registered to control this pest. However, translaminar insecticides such as Admire (imidacloprid) and Assail (acetamiprid) may also be efficacious against this pest.