American caterpillar infestation


This parasite of North American origin, was introduced in Europe in 1940 and quickly spread to Italy between 1975 and 1977 through means of transport, causing serious damage to broadleaf trees in urban green areas, along roads and railway lines. During the autumn the American caterpillarreaches a length of 1.9 cm. The members of this type live in gregarious form, they weave a common net extended to different leaves or whole branches of trees, on which they spend their period of development; Once all the leaves of the trees have been devoured, they settle in another. They are usually dark green, or even yellow with black stripes and covered with long coarse hairs, in fact in Latin America they are also called hairy or woolly caterpillars. The larvae feed in huge nests and are able to completely defoliate trees and shrubs.

Life cycle

The number of generations per year depends a lot on latitude. Populations in the south will be able to complete four generations in a year, while in the north only one life cycle will be completed. The adults are black-speckled white butterflies and emerge as early as March in the south, but they don’t fly until late spring or early summer in the northern areas. Mostly, adults appear from May to August to deposit their eggs (pale green in color) on the underside of the leaves. The larvae are yellowish-brown in color with a black head (especially in the northern regions) or red (in the southern regions) and a gray back, covered with long black and white hairs. At maturity they reach a length of 30-35 cm. The pupal stage overwinters in the bark at the base of the trees. It is dark brown in color and about 10mm long. The thin brown cocoon is made of silk with intertwined pieces of debris.

Damage caused

The larval stage of this parasite skeletons and consumes the leaves. They can defoliate a tree, but they can rarely kill it. They do not damage the tree noticeably, but they reduce its ornamental value. The American caterpillar is also known as a sericulture pest due to its preference for mulberry leaves. Caterpillars can build large silk curtains that sometimes grow on several branches (they usually only attack a few limbs or parts of the limbs on larger trees). The larvae make wide, shallow feeding routes on the surface of the fruit. Fruit on the defoliated limbs can be stunted and skimpy. In the course of their development, American caterpillars are capable of making distinct sharp movements in unison if the nest is disturbed.

American Caterpillar Infestation: Remedies

You can fight these caterpillars through the use of natural and chemical products. In the first case, various species of natural enemies can help manage this insect. Birds and some predatory insects attack the larval stage and the eggs. A mechanical method is also possible, which involves pruning the attached branches, in case the canvases have not become too large. If you want to use a chemical approach instead, you can apply an insecticide (when the webs and larvae are still small). The application is usually carried out in July and there is no need to treat the whole plant, but only the parts where there are cobwebs. However, care must be taken, because pesticides are poisonous. It is advisable to read and follow the directions and warnings on the labels,

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