Walnut moth
Walnut Hurdles, scientifically known as *Atrijuglans hetaohei Yang*, are also commonly referred to as "Walnut Black." These pests are primarily found in walnut-growing regions such as Hebei, Henan, Shanxi, Shaanxi, Gansu, Sichuan, and Guizhou. In particular, they are widespread and cause significant damage in the walnut production areas of the Taihang and Yanshan Mountains in Hebei, the Jindongnan and Jinzhong regions of Shanxi, and the Guanzhong and southern Shaanxi areas of Shaanxi.
The larvae of the Walnut Hurdle bore into the fruit, feeding inside and creating tunnels while leaving behind frass. A clear or amber-colored droplet often appears at the entry point, and as the green outer layer shrinks and rots, the fruit surface darkens and becomes shriveled, leading to a high rate of fruit drop.
Morphological Features:
Adults measure 5 to 8 mm in length with a wingspan of 12 to 14 mm. They have a dark brown, shiny body, red compound eyes, and pale brown antennae. The lower lip is well-developed, silvery white, and curved upward over the head. Their wings are long and narrow, with long cilia. There are two half-moon-shaped white spots on the forewings at one-third the distance from the base, along with a small white spot (sometimes barely visible). The abdomen has black and white scales, and the legs are white, with the hind legs being particularly long. The thorax and abdominal segments have ring-shaped black spines. When at rest, the wings are raised slightly to the sides and rear.
Eggs are oval, measuring 0.3 to 0.4 mm in length. Initially milky white, they turn yellowish-white, yellow, or light red before hatching, eventually becoming reddish-brown. The larvae start at about 1.5 mm in length, milky white with a tan head. Mature larvae grow to 7.7 to 9 mm, with a dark brownish-white body, a dark brown head, and a slightly pinkish underside. They have sparse white bristles.
Pupae are spindle-shaped, 4 to 7 mm long, and yellow-brown. The cocoons are elliptical, 8 to 10 mm in length, brown in color, and often stick to grass and fine soil particles.
Life Cycle and Habits:
In the southwestern walnut-growing areas, the Walnut Hurdle completes one generation per year. In Shanxi and Hebei, it also has one generation, while in Henan, there are two generations annually. Mature larvae burrow into the soil 1 to 2 cm beneath the canopy. Overwintering occurs in cracks under stones and at the base of trunks. In Hebei, wintering larvae emerge from early June to late July, with peak activity in early June lasting about seven days. Adults appear from early June to early August, with peak activity between late June and early July. Larval feeding begins in mid-June, sometimes as early as early June. Mature larvae begin fruit infestation in mid-July, and by early August to late September, they continue feeding inside the fruits.
In Mianyang, Sichuan, overwintering larvae start to pupate in early April, with peak emergence in mid-May to late May, and the pupal stage lasting 7 to 10 days. Overwintering adults first appear when the fruit reaches 6–8 mm in diameter, with peak activity in late April to mid-May, and the end of the adult stage occurring in mid-to-late June. Larvae are most active in mid-May to early May. The first generation of adults emerges in June, and second-generation larvae appear in late June.
Adults are slightly phototactic, preferring the lower parts of the canopy for mating and egg-laying. Most eggs are laid in the gap between two fruits, followed by those on the stem or petiole. Each fruit can contain 1 to 4 egg capsules, with more appearing later, sometimes up to 7 or 8 per fruit. A single female lays 35–40 eggs. Adult lifespan is around one week, and the egg stage lasts 4–6 days. After hatching, larvae crawl on the fruit surface for 1–3 hours before boring into the fruit. One fruit may host 5–7 larvae, with up to 30 individuals. Infestation takes 30–45 days to complete. Once the fruit falls, larvae burrow into the soil, and during harvest, about 80% of larvae remain in the fruit, covering them for winter. Some may be brought into the sun during harvesting.
Control Methods:
1. Deep plowing under the tree canopy in late autumn or early spring can destroy overwintering larvae and prevent adults from emerging. 2. Canopy spraying should be done during the adult egg-laying and larval hatching periods. Use 50% chlorpyrifos EC or 50% phoxim EC diluted 1000 times, or 2.5% beta-cyfluthrin emulsifiable concentrate diluted 3000 times. Apply 3 sprays in total, targeting larvae before they infest the fruits. 3. Ground application involves spraying 50% phoxim EC around the trunk before adult emergence, using 0.5 kg per mu, or applying 4% insecticide powder at 0.4–0.75 kg per mu to kill soil-dwelling adults. Applying phoxim EC or insecticide powder under the canopy during the larval eradication period is also effective. 4. Removing damaged and blackened fruits promptly reduces the population of the next generation by eliminating larvae before they mature.
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