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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 China, including Heilongjiang, Liaoning, Hebei, and Jiangsu. This pest primarily affects the cones, young shoots, and tender branches of Pinus koraiensis and other coniferous trees, leading to reduced seed production and poor quality of the seeds. The damage caused by this insect can significantly impact the growth and development of Korean pine and red pine.
The larvae of Dioryctria sylvestrella bore into the pine cones and young shoots, causing dead tips, replacement of main shoots with side shoots, and the formation of bifurcations. They also damage the base of the apical buds on the shoots, which results in the death of the buds and failure of new shoot growth in the following year. Such infestations seriously hinder the normal development of the trees.
Morphologically, the adult moth has a body length of approximately 15 mm and a wingspan of about 28 mm. The antennae are filamentous and covered with dense brown short hairs. The forewings are silvery gray with black and white scales, while the basal and inner transverse lines are connected at the base of the trailing edge and covered with a mix of black and white scales. The outer transverse line appears as a white, wavy band, and the inner and middle lines are edged with brown scales. A white kidney-shaped spot is present diagonally behind the lateral line, and the outer edge of the wing is lined with white scales and gray hair. The hind wings are pale gray. The abdomen is gray-brown with silver and copper scales, and the legs are black with white and black scales.
The eggs are oval in shape, measuring about 0.7 mm in length, and are dark red in color. The larvae grow up to 21 mm in length, with a head width of 1.2 mm. Their coloration is typically grayish brown or dark gray. The head is dark brown, while the thorax and abdomen have a lighter, more vibrant hue. The larvae have circular bristles on their bodies, with the pronotum having a black back and a central gray line. Each segment has three pairs of black tufts, and the midline of the fourth segment has one set of bristles. Under the valve line, there are two short bristles that become longer after hatching. The larval prolegs have two rows of hooks.
The pupal stage is oval, measuring about 15 mm in length and 3 mm in width. It is yellowish brown in color and lacks any distinct segments or hips.
In terms of its life cycle, Dioryctria sylvestrella completes one generation per year in Heilongjiang, with larvae overwintering. Activity begins in April, and larvae mature by late May. Adults emerge from mid-June to early July, and egg-laying occurs in late June. The larvae hatch in early July and begin feeding before overwintering in October.
During April, as temperatures rise, the larvae become active and start feeding on the whorled branches and cones at the base of the shoots. They often enter through pruning cuts, mechanical damage, or lesions caused by pine rust. This leads to the formation of galls. When they attack the cones from the lower part, the damaged area exudes a transparent resin and brown frass. By late May, mature larvae feed on the xylem of the shoots, creating chambers and sealing the feeding holes with silk-like wood shavings. The pupal stage lasts around 17 days.
Adults emerge in mid-June and remain active for about 20 days. Mating and egg-laying occur in late June, and the larvae cause damage again in July. By late July and early August, the affected cones produce excessive resin, leading to visible death of the larvae, with a mortality rate as high as 74%. However, if there are multiple rainy days, the resin loss stops, and the damage becomes more severe. In October, as temperatures drop, the larvae overwinter beneath the galls.
This insect prefers areas with a canopy density of 0.7, particularly under broad-leaved trees. Young trees are generally not affected, but when the canopy density is maintained at 0.3, the damage rate on young Korean pines is only 0.1%. As light transmission increases, the damage rate rises, reaching 45% at higher levels.
For control, forest management should be strengthened. Creating a young forest under the canopy and retaining some broad-leaved trees can help increase canopy density and reduce infestation. During winter and spring, regular surveys of nurseries, young forests, and scattered trees should be conducted, and any infested areas should be promptly cut and burned. Additionally, removing heavy infestations and burning them is crucial.
Using black light traps is an effective method due to the moths' phototactic behavior. Chemical control options include spraying 90% trichlorfon crystals or 50% phoxim emulsifiable concentrate at a dilution of 1000–1500 times, or using 50% chlorpyrifos EC, 50% dichlorvos EC, or 50% phosphate EC diluted 1000 times. Commonly used pesticides include trichlorfon, phoxim, safrole, dichlorvos, and phosphorus rubber.