Walnut moth
Walnut Hurdles (Atrijuglans hetaohei Yang), also known as "Walnut Black," is a significant pest affecting walnut production in several regions of China. It is commonly found in provinces such as Hebei, Henan, Shanxi, Shaanxi, Gansu, Sichuan, and Guizhou. In particular, it is prevalent in the walnut-growing areas of the Taihang and Yanshan Mountains in Hebei, as well as in Jindongnan and Jinzhong in Shanxi, and in the Guanzhong and southern Shaanxi regions. This pest causes considerable damage, especially in these key walnut-producing zones.
The larvae of this species bore into the walnut fruits, feeding on the inner tissues and creating tunnels. As they feed, they leave behind frass inside the fruit. A clear or amber-colored droplet may appear at the entry point, and the outer green peel begins to shrink and turn black, leading to fruit discoloration, shrinking, and eventual dropping. This results in substantial yield losses for farmers.
Morphological Features:
Adults measure 5–8 mm in length with a wingspan of 12–14 mm. They are dark brown and shiny, with red compound eyes and pale brown antennae. Their lower lip is silvery white and curved upwards over the head. The wings are long and narrow, with long cilia. On the forewings, there are two half-moon-shaped white spots near the 1/3 mark, along with one small white spot that may be barely visible. The abdomen has black and white scales, and the hind legs are white and elongated. The front legs have ring-shaped black bristles. When at rest, the wings are held sideways and slightly backward.
Eggs are oval, about 0.3–0.4 mm long, initially milky white, then turning yellowish, yellow, or light red before hatching into reddish-brown color. Larvae start at 1.5 mm in length, milky white with a tan head. Mature larvae reach 7.7–9 mm, with a dark brownish-white body, a dark brown head, and a slightly pinkish underside. They have sparse white hairs.
Pupae are spindle-shaped, 4–7 mm long, and yellow-brown. The cocoon is elliptical, 8–10 mm long, and often covered with grass and soil particles. The pupal stage lasts 7–10 days.
Life Cycle and Behavior:
This pest typically completes one generation per year in the southwestern walnut regions, but two generations can occur in Henan, and one in Shanxi and Hebei. Overwintering occurs in cracks under stones or at the base of tree trunks. In Hebei, larvae emerge from late May to July, with peak activity in early June lasting about a week. Adults appear from early June to early August, with peak activity between late June and early July. Larvae begin damaging walnuts in mid-June, sometimes earlier, and continue until late September. In Mianyang, Sichuan, overwintering larvae start emerging in early April, with peak emergence in mid-May. Eggs hatch within 4–6 days, and larvae take 30–45 days to develop inside the fruit before falling to the ground.
Adults are slightly attracted to light and tend to mate in the lower parts of the canopy. They lay eggs in the gaps between nuts, as well as on stems and petioles. Each female lays 35–40 eggs, and the adult lifespan is about a week. The second generation of larvae primarily feeds on the mesocarp when the endocarp hardens, causing the fruit surface to darken and become sunken. By harvest time, around 80% of the larvae are still inside the fruit, while some may fall into the soil during collection.
Control Methods:
1. Deep Soil Tilling: In late autumn or early spring, plow the soil under the tree canopy to destroy larvae and prevent adults from emerging. 2. Canopy Spraying: During the adult egg-laying and larval hatching periods, spray insecticides like 50% chlorpyrifos EC or 50% phoxim EC diluted 1000 times, or 2.5% cypermethrin EC diluted 3000 times. Apply three times, spaced 10–15 days apart, to control larvae before they infest the nuts. 3. Ground Application: Before adult emergence, spray 50% phoxim EC on the ground around the trunk at 0.5 kg/mu, or apply 4% carbofuran powder at 0.4–0.75 kg/mu. These treatments effectively target soil-dwelling adults and larvae. 4. Remove Infested Fruits: Regularly remove damaged or blackened nuts to reduce the population of the next generation. This helps lower the infestation pressure in subsequent seasons.
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