This is a serious pest of apple trees in some areas of coastal BC. It is an introduced pest from Europe first observed in Fraser Valley in the early 1990s.
There are four generations per year in this area. It overwinters as pre-pupae or pupae in cocoons in the soil, and occasionally in curled leaves or other protective sites beneath host trees.
Adults usually begin to emerge in early May. During their one-week life span, they mate and lay eggs on the edge of terminal apple leaves. Females generally lay 30 – 40 eggs per leaf and eggs take 2-10 days to hatch, depending on temperature. Larvae feed on the upper surface of leaves for 2-3 weeks causing the leaves to roll, enclosing the larva. In the early stages the rolled leaves can be unrolled exposing the larva. Young larva are tiny (full grown they are 1.5 to 2.5 mm long), legless, white (almost clear) progressing to yellow and then orange over a 4 week period before dropping to the ground to pupate .The pupa of the last generation in the fall stays in the soil to emerge the following May.
This is primarily a pest of shoot tips of nursery or small apple trees, but it will infest shoot tips of larger trees. Once established it is a major cosmetic problem for espalier and container grown trees.
The female sex pheromone for this pest has been identified so it is possible to trap males for monitoring. Trapping is unlikely to be of much value to home gardeners unless you plan to spray to kill the adults, and this is not only difficult but may get you into more trouble than the midge has already caused. The organic pesticide of choice is pyrethrin. Pyrethrins are very effective insecticides; however, they usually kill the target insect as well as beneficial insects and predator mites, often leading to mite flare ups.
Control: In gardens this pest is best treated as an annoyance and ignored hoping for a bit of biocontrol from predator insects. Minute pirate bugs, Orius spp. and other bugs have been observed feeding on apple leaf midge larvae in our area.
Agriculture Canada is researching the potential to release a predators for this pest. In Eastern Canada, the introduced European parasitoid Platygaster demades has been shown to effectively reduce (40-90%) the first generation.
If you only have a few small trees and the curled leaves irritate you, remove them as soon as they start to roll and destroy them. Destroying the larva will reduce the number that emerge from under your trees for the next generation. Picking off the new leaves on an apple shoot will not do any harm to the tree as long as you don’t damage the growing point. If you are growing a few nursery or espalier trees, picking these leaves off could be an advantage as this practice is known to stimulate lateral branching.
Commercial nursery producers should check out the references below:
YouTube for Commercial Apple Packing (please note: this is a commercial video by a New Zealand company. I have no affiliation with this company)