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Leaf Curling Midges

In recent years apple growers have been seeing an increased amount of leaf curling midge damage in their orchards. The leaf curling midge (Dasineura mali) is a European pest that arrived in North America in the 1960's.

The leaf curling midge overwinters as a pre-pupa or pupa in silken a cocoon in the soil, or in curled leaves. Adults begin to emerge in late May to early June. The adult 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 feed on the upper surface of leaves for 2-3 weeks. 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 20-30 larvae, however as many as 500 larvae can be found in an infested leaf. The margins of infested leaves are rolled in towards the mid-vein of the leaf (Fig 1) and the leaves become purple or red and brittle before dropping from the tree. Pupation occurs in early July and larvae from the second generation are present in orchards in August. Larvae feed for up to 4 weeks before dropping to the ground to pupate. Apples are the only reported host for this particular species of midge. Varieties with lush terminal growth may be preferred due to the availability of egg laying sites, however all cultivars are susceptible to infestation.

Leaves affected by apple leaf curling midge larvae

These insects are not considered to be an economic pest of apples and are not a concern on mature apple trees. 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 (diazinon) applied against key pests. These insects could be becoming more prevalent in orchards as we move away from using broad spectrum insecticide programs.

The only way to monitor for the leaf curling midge is to inspect young trees for the presence of curled leaves, and orange maggots in the terminals. There is no economic threshold for managing this pest.

Orius spp. and mullein bugs will feed on leaf curling midge larvae. In Nova Scotia and New Brunswick the European parasitoid Platygaster demades has been shown to parasitize 40-90% of the first generation leaf curling midges. However the asynchronous development of the pest and parasitoids decreases parasitism to only 1-3% in the second generation.

It is very difficult to manage this pest using insecticides since the midges are well protected inside the curled up leaves. Currently Ripcord 400EC is the only product registered to control this pest. However, broad spectrum products applied to manage other insect pests in the orchard may also be efficacious against apple leaf curling midge larvae.