The name of the frost moth comes from the fact that the pupae hatch at low temperatures and the feeding technique: In order not to be disturbed during their meal, the caterpillars entangle themselves between the leaves. A distinction must be made between the small frost moth (Operophtera brumata) and the large frost moth (Erannis defoliaria) – although the larger butterfly is found less often in gardens and therefore causes significantly less damage. For this reason, this article is dedicated to the small butterfly, whose caterpillars have a big appetite: their diet includes not only fruit trees (preferably apple, pear, cherry and plum), but also ornamental woods such as maple and linden. How you can recognize a frostbite infestation more quickly and what you can do about it is summarized below.
The frost moth is a small butterfly with brown robes. In contrast to females, only males are able to fly. Both emerge when the first frost hits – around mid-October. After mating occurs, females lay up to 300 eggs near buds in the tree bark. The eggs are initially green and over time turn orange to red. When spring sets in and the first buds open, the larvae of the frost moth hatch and go looking for food. Their method of locomotion is unmistakable: they only have “feet” on their stomachs and at the end of their bodies, which they pull together like a kind of cat’s hump and push them apart again in order to move forward. After the caterpillars have filled their stomachs between April and June, they abseil themselves on a thin spider thread from the infected trees to the ground and pupate underground. The pupae stay there until late autumn before they emerge as adult frostbittens and a new life cycle begins.
If you discover the frost moth caterpillars in spring, it is too late to take preventative measures. In this case it makes more sense to fight the butterfly directly. On the one hand, you can use special preparations against butterfly caterpillars that contain the active ingredient Bacillus thuringiensis (a bacterium). The spray is applied to the affected areas and is ingested by the caterpillars when they eat flowers, leaves and buds. However, only use the product when the outside temperature is at least 15 degrees. Before that, the offspring of the frost moth are not so hungry and are actively looking for food. Or you can use alternative products to combat frostbite that contain other active ingredients – for example neem oil or indoxacarb.
So-called glue rings offer another way to combat frostbite. What exactly this is and what you should pay attention to is explained in the next section on preventative measures.
To prevent the small frost moth from infesting your fruit and ornamental trees, you can take preventive measures – for example by encouraging the butterfly’s natural predators: great tits can eat hundreds of caterpillars in just one day. To attract them to your garden, you should attach suitable nesting boxes to the trees. Another option is to stop the flightless females, who have to crawl up the trunks to attract the flying males. To do this, attach special glue rings as close as possible to the trees as well as to all support posts and directly neighboring trees at the beginning of October. Replace them if they are dry or damaged. Or use caterpillar glue, which you apply directly to the bark with a brush. In both cases, the female frostbite remains stuck to it and mating does not occur.
Important note: Remove the glue rings in spring so as not to endanger any beneficial insects.
Source: My Beautiful Garden
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