Leopard moth

The leopard moth (Zeuzera pyrina) is a member of the Cossidae family within the order Lepidoptera. The adult moth is large, with a wingspan of up to 70 mm, characterized by white wings covered in numerous distinct blue-black spots.

The moth's body is densely covered in hair. Unlike the adult, the larvae (caterpillars) possess a yellowish-white body marked with small black bumps and a dark brown head capsule. As they grow, these larvae can reach 60 mm in length and are extremely agile.

The life cycle of the leopard moth typically spans two years. During this period, the larvae live inside tunnels they excavate within the tree's wood, which provides them with both nutrition and protection from most predators.

Pupation occurs in the spring directly inside the wood tunnel. Once mature, the pupa pushes itself toward the opening before the adult moth emerges to start the reproductive cycle, usually lasting from June through August.

Females lay eggs either individually or in small clusters in bark crevices, near buds, or at branch junctions. Once hatched, young larvae initially feed on leaf stalks or tender green shoots before burrowing deeper into the main branches.

The leopard moth is a polyphagous pest affecting a wide variety of fruit trees including apple, pear, plum, and cherry. It also infests ornamental trees such as maple, lime, ash, and lilac, making it a threat to both orchards and landscape trees.

Damage is caused by larvae that bore deep galleries into the woody tissue. These tunnels interrupt the vascular system, leading to poor sap flow, stunted growth, and the eventual death of affected branches or the entire tree.

Young trees are at the highest risk of mortality. If a larva bores into the main trunk or the crown leader, it can cause the entire tree to die, especially if the structural integrity is severely compromised.

Infested branches become structurally weak and are prone to breaking during high winds or heavy fruit loads. This physical damage creates entry points for fungal and bacterial pathogens, exacerbating the overall decline.

Leopard moth infestations are often hidden, making early detection difficult. By the time symptoms like wilting or branch dieback appear, the larvae have often caused irreversible structural damage to the tree.

The most reliable sign of an infestation is the presence of small holes in the bark, accompanied by piles of frass—a mixture of wood shavings and reddish-brown caterpillar excrement—accumulating on the bark or at the base of the tree.

During the growing season, you may notice sudden wilting and dieback of the tips of young shoots. This happens because young larvae are feeding on the center of the succulent stems, effectively killing them from within.

Sap or gum often oozes from the entry holes as a defense response by the tree. In some cases, light webbing can be observed around the tunnel entrance, holding together the fine debris produced by the larva.

In autumn, a clear sign of an infested branch is the presence of "flags"—branches with prematurely yellowed or brown leaves that stand out against the rest of the green canopy, indicating interrupted vascular flow.

Inspection of the trunk and branch crotches may reveal small, circular entry points. These tunnels are often kept clean by the larvae, which push their frass out to prevent the galleries from becoming clogged.

Effective management begins with strict sanitation: prune and burn all infested branches immediately to kill the larvae before they progress to the pupal stage or emerge as adults.

• Regularly clear loose bark to inspect for entry holes.
• Use a thin wire to physically destroy larvae in accessible tunnels.
• Inject systemic insecticides into the tunnels using a syringe.
• Seal entry holes with grafting wax to prevent moisture and secondary infection.
• Deploy pheromone traps to monitor adult flight and time insecticide sprays correctly.

Biological control using entomopathogenic nematodes injected into the tunnels has shown promising results, as these microscopic worms seek out and infect the larvae within their galleries.

Maintaining optimal tree health through proper irrigation and nutrition helps trees recover from minor damage and improves their overall resistance to wood-boring pests.

Chemical control is most effective during the peak flight of adult moths and the brief period when newly hatched larvae crawl on the bark surface before entering the wood, as they are susceptible to contact insecticides at that stage.