Aromatic wood moth
Cossus cossus L., commonly known as the poplar cocoon moth or red-harex insect, is a significant pest found in northeastern, northern, and northwestern China. This species primarily affects a wide range of host plants, including walnuts, apples, pears, peaches, apricots, as well as trees like poplars, willows, sorghum, birch, coriander, and hazel.
The damage caused by this insect is distinctive. The larvae bore into the xylem, creating shallow tunnels or trough-like pits on the surface. In the early stages, multiple larvae—often more than 10 or even dozens—can be found feeding together. As they grow older, the larvae tend to disperse within the same section of the trunk, feeding on the inner pith and gradually forming thick, irregular tunnels. A notable feature is the secretion of an aromatic liquid, which gives the insect its common name.
Regarding its physical characteristics, adult Cossus cossus moths are generally taupe in color with a darker abdomen. They measure about 30 mm in length and have a wingspan of 56–80 mm. Females are typically larger than males. Their antennae are dentate, and their compound eyes are dark brown. The forewings are grayish-white with a grayish-brown leading edge and dense brown wavy patterns. A prominent, thick ripple runs from the trailing edge to the leading edge of the wings.
The eggs are initially white but turn dark brown before hatching. They are nearly oval in shape, measuring approximately 1.5 mm in length and 1.0 mm in width. The egg surface features longitudinal ridges with transverse lines between them.
The larvae are flat and cylindrical, starting at around 3–4 mm in length when first hatched and growing up to 56–80 mm by the end of their development. The dorsal side of the thorax is red or purple, shiny, while the ventral surface is yellowish or light red. The head is dark purple with irregular fine lines, and there is a pair of large, purplish-brown stripes on the pronotum.
The pupal stage involves two types of cocoons: one long and slightly curved, measuring 50–70 mm in length and 17–20 mm in width, made from soil particles. Another form is a flat, round structure about 40 mm long, 30 mm wide, and 15 mm thick, created by the last-instar larvae after they leave the tunnel and spit out material near the knot. These cocoons are relatively loose in texture.
The life cycle of Cossus cossus varies depending on the region. In areas such as Henan, Shaanxi, Shanxi, and Beijing, it completes one generation in two years, while in Xining, Qinghai, it may take three years. The larvae overwinter in the soil near the base of the tree or in the trunk. In April to May, the mature larvae emerge and pupate, with adults emerging in June to July. Adults are nocturnal and attracted to light. Eggs are laid about 1.5 meters below the base of the trunk, in cracks, or at the junction of roots and stems. Each female lays an average of 245 eggs in clusters, with each cluster containing 50–60 eggs.
After hatching, the larvae drill into the bark through wounds, cracks, or old holes, leaving behind finely divided brown wood chips. Initially, they feed under the bark, separating the xylem from the cortex and creating a trough-like pit. As they grow, they move deeper into the trunk, feeding on the pith and creating irregular tunnels. By October, they retreat into their tunnels to overwinter. The following year, they continue feeding until they become fully mature. From late September to early October, the larvae exit the tunnels and burrow into the soil about 10 cm deep near the roots or a few meters away from the trunk. When disturbed, mature larvae can secrete an aromatic liquid, reinforcing the origin of their name.
To manage infestations, several preventive measures can be taken. First, during the adult mating period, coating the trunk with clay agents can help prevent egg-laying. Second, during the larval feeding phase (5–10 days), applying a 40% Dimethoate emulsion diluted 25–50 times and injecting it into the entry holes can effectively kill the larvae. After application, sealing the hole with mud helps ensure the solution stays in place. Third, if larvae are detected beneath the bark, manually removing the affected bark can help eliminate them directly.
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