Have you ever seen strange bits sticking out of your apple tree in spring?
Or, moths fluttering around your tree on a summer afternoon? You might want to take a closer look. Those bits may be discarded pupal casings from apple clearwing moths, and these pests can kill your tree.
Also known as red-belted moths, apple clearwing moths (Synanthedon myopaeformis) are native to Europe, North Africa, and the Near East. They were first seen in North America in 2005, in Canada. Now, Canadian entomologists estimate that the majority of host trees in British Columbia are infested. By 2007, these pests had made their way to Washington state. It’s only a matter of time until they spread further.
And apple trees aren’t the only ones vulnerable to this pest. If you grow almonds, apricots, cherries, crabapples, peaches, pears, plums, or quince, you should know about apple clearwing moths. These invasive pests also attack hawthorn and mountain ash trees and are attracted to showy milkweed plants.
Damage caused by apple clearwing moths
The moths themselves are harmless. It’s their larvae that cause significant damage, especially to older trees. Caterpillars burrow under the bark, entering at burr knots, grafts, pruning wounds, injured branch collars, and areas damaged by tree supports left in place for too long.
Larval feeding can kill young trees. Trees that survive often have weakened limbs, reduced fruit set, and early leaf drop. These conditions make trees susceptible to other pests and diseases and more vulnerable to drought stress and frost damage.
Apple clearwing moth lifecycle
These pests have a 2-year lifecycle. Female moths feed on nectar early to mid-summer, laying up to 250 eggs singly in crevices. When the eggs hatch, larvae burrow into the cambium layer. They feed on sap found in the phloem for the next two years. As they eat, they create shallow, winding galleries that weaken the tree. They also feed on new leaf and flower buds. In spring, you may be able to see the frass (bug poop) pushed out of these galleries by the larvae. [How about that? Even insects perform spring cleaning.]
Larvae spend the winter protected in these tunnels, pupating the next spring. When pupae are ready to break free and fly, they push themselves through these frass openings. In addition to these discarded pupal cases, you may also see tiny holes (about half the diameter of a pencil lead) around the base of an infested tree.
Apple clearwing moth description
It should come as no surprise that clearwing moths have transparent wings. Unlike most moths and butterflies, clearwing moths do not have scales on their wings. They do have short, bushy tails, though!
Apple clearwing moths have narrow, bluish-black bodies. Their forewings are slender and their hindwings are short. They have wingspans of ¾ - 1” wide and distinct reddish-orange bands around their bellies. Larvae are ½- ¾” long, a dirty white color with a reddish-brown head. Pupae are ½” long and pale yellowish-brown.
Apple clearwing moth control
Preventing this problem is much easier than fixing it. Start by making sure your pruning cuts are clean and flat and that they do not cut into the branch collar.
If you believe your trees have become infested with apple clearwing moths, do not use wires to probe the holes the way you might go after squash vine borers in your zucchini plants. Infested trees already have enough damaged areas. They don’t need more.
You may be able to reduce the number of adult moths emerging from cocoons by spraying Bacillus thuringiensis (Bt). Applications of cottonseed oil have also been shown to be helpful.
You can use the same yellow pheromone traps that attract male peach tree borers or make your own traps by baiting bottle traps with grape juice. To make a bottle trap, simply cut the top off a liter soda bottle and invert the top into the base. Tape the two parts together, creating a funnel. Male and female clearwing moths will be attracted to the grape juice but unable to find their way out of the trap. A mix of 8 parts water, 1 part apple juice, 1 part vinegar, and a little sugar has also been shown effective.
Just remember, if you put out attractants, whether food or pheromonal, you will be attracting moths to your garden. There are insecticides rated for use against apple clearwing moths, but they have their own drawbacks. Only do these things if you need to.
If you believe you have apple clearwing moths on your property, please contact your local County Extension Office right away. And try to capture a specimen.
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