Box tree moth eggs: identification & control

The box tree moth can camouflage itself very well. Even the tiny box tree moth eggs are hard to spot. Find out all about these pesky boxwood pests and what measures you can take to prevent and combat them.

Although the box tree moth (Cydalima perspectalis) can cause extensive damage, it lives most of its life cryptically, that is, hidden and protected from predators and humans. Detecting a box tree moth infestation early on gives you the upper hand and your boxwoods (Buxus) a greater chance at survival. In the following article, we discuss how to recognise and find box tree moth eggs on your boxwoods.

Detecting box tree moth eggs at an early stage gives you the best chance at a timely control. Read on to find out when box tree moths lay their eggs, how to recognise them and how to remove or kill them.

When do box tree moths lay their eggs?

In our part of the world, there are two or more generations of the box tree moth each year, meaning they lay their eggs at least twice a year. The time it takes for the caterpillars to develop into adult moths capable of mating depends on the weather. As a result, it is not possible to name a fixed time of year when the box tree moth lays its eggs. The only way of knowing when exactly eggs will appear on your plants is by using a box tree moth trap to observe when the moths begin to fly. Our Plantura Box Tree Moth Traps are available to purchase in our online shop. These traps help to detect a box tree moth infestation at an early stage. See the table below for a general idea of the box tree moth life cycle. In a nutshell, the overwintered caterpillars develop and, after mating in June and July, lay eggs on the host plant – often our beautiful boxwoods. This same cycle then repeats around September. The larvae hatching from these eggs hide in a protected area of the plant after nibbling away at the foliage a little and overwinter there in a web until the following spring.

Unfortunately for us, it only takes about three days for a box tree moth egg to hatch and for a new hungry caterpillar to appear. As the eggs are laid over a long period of time, it is not at all uncommon to find eggs and larvae around at the same time. As soon as you spot any moths or find them in your box moth traps, you will need to check your boxwoods for egg clutches on a daily basis.

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Tip: Depending on the weather, it is theoretically possible for there to be up to four generations of box tree moths in one year, as heat can greatly accelerate their development.

Recognising box tree moth eggs

In the eight days that a female box tree moth spends as an adult moth, she will mate and proceed to lay about 150 pale yellow, lentil-shaped eggs that are just a few millimetres in size. Box tree moths prefer to lay their eggs on the outer leaves of previously non-infested boxwoods. There they will lay around 20 eggs closely together on the underside of the leaf in so-called egg clutches or clusters. Shortly before hatching, black dots will appear on the egg. These are the heads of the larvae at the first larval stage. There are six larval stages in total. After hatching, the pale yellow caterpillars will set off to feed on the inner, protected areas of the host plant.

Box tree moth control

There are three effective ways to get rid of box tree moth eggs:

Controlling box tree moths by pruning

As it is the larvae feeding on the boxwood leaves that causes the damage, killing or removing box tree moth eggs before they hatch is an effective way of preventing damage. However, this can be quite difficult and there is only a short time frame within which to do this as the eggs do not take long to hatch. A simple and efficient method is to prune the boxwood no more than two weeks after you notice the moths flying. At this point, the eggs and young larvae will still be on the outside of the boxwood, so can be removed by pruning the plant. After pruning your boxwood, place the removed foliage in a tightly closed bag and dispose of it along with the normal waste.

Controlling box tree moths with beneficial insects

Beneficial insects are another effective way of getting rid of box tree moths. There are several species of parasitic wasps of the genus Trichogramma that parasitise the box moth eggs, killing the life inside and preventing any new box caterpillars from hatching. You can buy wasp cards containing parasitic wasp eggs to hang in your boxwoods once the moths take flight. After hatching, the beneficial wasps seek out the box tree moth eggs and parasitise them. While this environmentally-friendly process has proven very effective in greenhouse trials, there are many factors which reduce its efficiency out in the open, including wind or predators. As the wasps are free to migrate outside, the presence of eggs from other insects (known in this case as non-target organisms or NTOs) could also compromise results as the beneficial insects may prefer to parasitise these instead.

Protecting boxwoods from box tree moths

You can also use protective nets over your boxwoods to protect them from box tree moths. This will help stop the box tree moth eggs from being laid on the plant in the first place. Secure nets over each boxwood for three weeks from April to September (or whenever you notice the moths infesting your boxwoods). While the net may be unsightly, it can help keep your boxwood safe from these destructive pests. Even once the egg-laying period has elapsed and the larvae have taken over your boxwood, all is not lost.