Large tortoiseshell

Systematic position: The Large tortoiseshell (Nymphalis polychloros) is a butterfly belonging to the order Lepidoptera and the family Nymphalidae. While aesthetically pleasing as an adult, the larval stage of this species acts as a significant defoliator in various agricultural and forestry settings.

Affected crops: The larvae are highly polyphagous, feeding on a wide range of fruit trees, including apple, pear, cherry, and plum. Beyond orchards, the species frequently colonizes broad-leaved trees like elms, willows, poplars, and birches, often causing visible damage to host canopies.

Biology and life cycle: This species overwinters as an adult butterfly in sheltered crevices, such as tree bark or buildings. In early spring, females deposit clusters of eggs onto the twigs of host plants. Upon hatching, the gregarious larvae live together in communal silken nests, which they enlarge as they consume surrounding foliage.

Damage and economic significance: The damage is primarily caused by the feeding behavior of the larvae. Young caterpillars skeletonize the leaves, while older instars consume entire leaf blades, leaving only midribs. Severe infestations can lead to significant defoliation, stressing the trees and reducing their photosynthetic capacity and overall vigor.

Protection measures: Effective management involves early detection and physical removal of the communal nests before the larvae disperse. Recommended strategies include:

• Regular inspection of branches in spring to locate and remove egg batches or young larval webs.
• Application of biological insecticides, such as Bacillus thuringiensis, which are effective against young instars.
• Targeted use of registered chemical insecticides if local population thresholds are exceeded and crop damage becomes critical.