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Apple leaf midge is an introduced pest from Europe first observed in Okanagan Valley in 2003 but present in Fraser Valley since early 1990s.
Larval feeding causes leaves to curl tightly upwards and the tissue to thicken, often displaying a purplish color (Figs. 1, 2). 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.
|Figure 1. Apple leaf midge damage. (H Philip)||Figure 2. Apple leaf midge damage. (H. Philip)|
Larva - White to orange-red (depending on age), legless, maggots up to 3 mm long (Fig. 3).
|Figure 3. Mature apple leaf midge larvae. (H. Philip)|
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.
There are at least two generations per year in British Columbia. It is distributed throughout the Fraser Valley and in central parts of the Okanagan Valley. 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 of leaves 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.
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. In the UK, researchers have identified female sex pheromones for trapping males. A threshold of 30 adults/trap/week is used for timing insecticide sprays.
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 BC.
There are no cultural methods that will adequately reduce the risk or severity of apple leaf 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.
Ripcord (cypermethrin), Decis (deltamethrin) and Movento (spirotetramat) are registered for control of apple leaf midge. These products are not effective against larvae in leaf curls. Ripcord and Decis are harmful to beneficial insects and mites and would lead to mite flare ups. Field trials in Ontario indicated Movento provides good control of the midge at petal fall timing. Application interval for Movento is a minimum of 14 days with a maximum of 2 applications per year.