Ministry of Agriculture

Apple Leaf Curling Midge

Hosts

Apple. First observed in Okanagan Valley in 2003 but present in Fraser Valley since early 1990s.

Damage

Larval feeding causes leaves to curl tightly upwards and the tissue to thicken, often displaying a purplish color. Damage is easily confused with aphid infestations. Feeding on terminal leaves reduces terminal growth and may distort limb growth; leaves may drop prematurely. There is no evidence of reduced fruit quality or quantity in bearing trees. Primary impact is to delay or stunt structural development of nursery and young bearing trees.

Apple leaves with rolled, reddish edges
caused by apple leaf midge larvae
Apple leaf midge larvae

Identification

Larva - White to orange-red (depending on age), legless, maggots up to 3 mm long.

Adult female - Delicate mosquito-like fly, dark brown body with reddish abdomen, about 2-3 mm long.

Adult male - Male resembles female but lacks reddish abdomen.

Life History

The life history of this insect in B.C. is unclear, but there are at least two generations per year. It is distributed throughout the Fraser Valley and in central parts of the Okanagan Valley. In Nova Scotia the apple leaf midge overwinters as pre-pupae or pupae in cocoons in the soil, and occasionally in curled leaves or other protective sites beneath host trees. Adults begin to emerge in late May to early June and during their one week life span, mate and lay eggs on the edge of terminal apple leaves. Larvae feed on the upper surface for 2-3 weeks. Pupation occurs in early July with second-generation larvae appearing in August. They feed for up to 4 weeks before dropping to the ground to pupate in the soil for the winter.

Monitoring

Inspect developing shoots of nursery and young trees less than 2-3 years old for curled, often purplish, curled terminal leaves containing white to bright orange maggots. There is no economic threshold. In the UK, researchers have identified female sex pheromones that attract males. There is ongoing work to determine threshold numbers in traps for timing insecticide sprays.

Control

Cultural - There are no cultural methods that will adequately reduce the risk or severity of apple midge infestations. Hand removal and destruction of infested leaves may help but removing terminal leaves can result in the same impact on tree development. Proper management of susceptible trees will help minimize the impact of the midge.

Biological - Pirate bugs actively feed on larvae (campylomma have also been observed within infested leaves). Native and introduced parasitoids attack midge larvae in New Brunswick but no information is available on parasitoids attacking apple leaf midge in B.C.

Chemical - The only products registered for the control of apple leaf curling midge are Ripcord (cypermethrin) and Decis (deltamethrin). These products are harmful to beneficial insects and mites and would lead to mite flare ups.

Updated February 2010


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