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Dioryctria sylvestrella (Ratzeburg) is a species of moth belonging to the family Pyralidae. It is commonly found in several provinces in northern China, including Heilongjiang, Liaoning, Hebei, and Jiangsu. This pest primarily targets the cones, young shoots, and saplings of Korean pine (Pinus koraiensis), causing significant damage that leads to reduced seed production and poor quality of the seeds.
The larvae of Dioryctria sylvestrella bore into the pine cones and young shoots, resulting in dead terminal growth, replacement of main shoots by lateral branches, and the formation of bifurcations. They also damage the base of the apical buds on shoots, leading to bud death and failure of new shoot development the following year. Such infestations severely hinder the normal growth of both Korean pine and red pine trees.
Morphologically, the adult moth has a body length of about 15 mm and a wingspan of 28 mm. Its antennae are filamentous and covered with dense brown short hairs. The front wings are silvery gray with black and white scales, while the basal area has white scales. The sub-basal and inner transverse lines meet at the base of the trailing edge and are covered with black and white scales. The outer transverse lines are white and wavy, while the inner and middle lines have brown scales along their trailing edges. A white kidney-shaped spot is located diagonally behind the lateral line. The outer edge of the wing is black, lined with white scales and gray hair. The hind wings are pale gray. The abdominal back features gray-brown, silver, and copper scales, while the legs are black with black and white scales.
The eggs are oval, approximately 0.7 mm long, and dark red in color. The larvae measure about 21 mm in length and 1.2 mm in head width. Their body color ranges from grayish brown to dark gray. The head is dark brown, while the thorax and abdomen are pale yellow with bright markings. The larvae have circular bristles on their bodies, with a black pronotum and a gray midline. Each segment has three pairs of black tufts, and the fourth segment has one set of bristles. Beneath the valve line, there are two short bristles that grow longer after hatching. The larval prolegs have two rows of hooks.
The pupal case is elongated, measuring around 15 mm in length and 3 mm in width. It is yellowish brown in color and lacks any visible legs or appendages.
In terms of its life cycle, Dioryctria sylvestrella completes one generation per year in Heilongjiang. The larvae overwinter and become active in April. By late May, they mature, and adults emerge between mid-June and early July. Mating and egg-laying occur in late June, with larvae hatching in early July. The larvae continue to feed and develop until October, when they enter winter dormancy under the galls formed on the trees.
During April, as temperatures rise, the larvae begin to move and attack the whorled branches and cones at the base of the shoots. They typically enter through pruning cuts, mechanical injuries, or lesions caused by pine rust. These wounds lead to the formation of galls. Damage to the cones starts from the lower parts, and the affected areas exude white transparent resin mixed with brown insect frass. By late May, mature larvae feed on the xylem of the shoots, creating chambers and sealing them with silk-like wood shavings. The pupal stage lasts about 17 days.
Adults emerge in mid-June and remain active for about 20 days. Mating and egg-laying take place in late June. In July, the larvae cause further damage, and by the end of July and early August, the affected cones release large amounts of resin, leading to high mortality among the larvae—up to 74% in some cases. However, if there are consecutive rainfalls, the resin loss stops, and the damage becomes more severe. In October, as temperatures drop, the larvae overwinter beneath the galls.
This pest prefers areas with moderate light levels, particularly in broad-leaved tree canopies with a density of around 0.7. Young trees are generally not affected, but when the canopy density is low—such as 0.3—the damage rate on young Korean pines can reach up to 0.1%. As light transmission increases, so does the damage, reaching 45% at higher light levels.
To manage this pest, several control methods are recommended:
1. **Forest Management**: During tending operations, create a young forest under the existing canopy and retain a certain number of broad-leaved trees to increase canopy density and reduce infestation. Regular surveys should be conducted in winter and spring to identify and remove infested trees, followed by burning to prevent further spread.
2. **Light Traps**: Use black light traps to capture adult moths, taking advantage of their phototactic behavior.
3. **Chemical Control**: For young larvae, apply insecticides such as 90% trichlorfon crystals or 50% phoxim emulsifiable concentrate diluted at 1000–1500 times. Other options include 50% chlorpyrifos EC, 50% dichlorvos EC, or 50% phosphate EC at a 1000-times dilution. Commonly used chemicals include trichlorfon, phoxim, safrole, dichlorvos, and phosphorus rubber.