The phenomenon of leaf loss of oak trees in most Lebanese regions is due to the feeding of the larvae of the gypsy moth insect on their leaves. However, the oak tree, known for its resilience, eventually recovers, as its shoots and leaves grow back in late June, when the insect reaches the end of its larval life.
The oak gypsy moth, or Lymantria dispar, belongs to the class of Lepidoptera butterflies, and is similar to the pine gypsy moth in its shape, and eating regimen consisting of forest tree leaves.
Female butterflies are distinguished by their white color and large size, while male butterflies are brown and relatively smaller than the females.
The color of the larvae varies according to the stage of growth and ranges from black to brown or gray while the worms are covered with thick hairs that may cause allergic reactions in some people.
1- Trees bare of leaves during the spring season
2- In the summer, especially from June to July, brown cocoons are found hanging on the trunk of the tree with a silk thread.
3- From July until March, the females lay their eggs in the form of a sponge on the tree trunk.
Insect life cycle
Mating season occurs in June.
The females lay eggs at the end of July and August under the branches and on the trunks. Eggs remain until the month of March and release the young larvae that feed on the leaves until June before turning into cocoons, weaving a silk thread and attaching themselves the head down until the spring to start a new life cycle.
The greatest damage occurs during the larval stage, where the larvaes devour the leaves of trees from the beginning of March until the end of June. This inevitabely affects the physiological growth of the tree.
The absence of control measures will inevitably lead to the death of the tree after two to three years.
- To reduce the spread of this insect, especially at the pre-mating stage, pheromone traps should be used. These traps attract adult males in the month of May.
- Bacillus Thuringiensis is a biological control measure to control the larval stage without affecting other beneficial insects such as honey bees in early May.
Eng. Akel El Sayegh