Rice Ridged Rice Butterfly
The scientific name of this species is *Parnara guttata* Bremer et Grey, which belongs to the order Lepidoptera, family Heteroidea. It is commonly known as the rice moth or rice worm. Although it is not reported in Xinjiang and Ningxia, it is widely distributed throughout the rest of China.
This pest has a broad range of host plants, including rice, wheat, corn, sorghum, barley, millet, bamboo, reeds, white wax trees, alfalfa, and foxtail. The larvae are particularly destructive, as they feed on the leaves and stems of these crops.
After hatching, the larvae climb to the edges or tips of leaves and roll them into cylindrical shapes, creating a protective shelter. This behavior makes them difficult to detect and control. The larvae can cause significant damage by feeding on the plant tissues inside their rolled shelters.
Morphologically, the adult moth has a body length of 17–19 mm and a wingspan of 28–40 mm. The body and wings are dark brown with a slight greenish tinge. The head and thorax are wider than the abdomen. The front wings feature 7–8 translucent white spots arranged in a semi-circular pattern, with a larger spot at the bottom. The hind wings have four small white transparent spots aligned in a straight or nearly straight line. Both the front and hind wings share similar markings.
The eggs are brown, hemispherical, and measure about 0.9 mm in diameter. They start off gray-green and later turn reddish. Each egg has a crown-like structure with 8–12 petals. The last-instar larvae are 27–28 mm long, with a brownish-yellow head. A distinct "mountain"-shaped brown mark is located in the center of the head. Their bodies are yellow-green with a dark green dorsal stripe and a brownish plate along the back. The pupae are light yellow, about 22–25 mm long, and nearly cylindrical with a flat tip.
In terms of life cycle, the number of generations varies by region. North of the Great Wall, there are 2 generations per year; north of the Yellow River, 3 generations; between the Yangtze and Yellow Rivers, 4–5 generations; south of the Yangtze River, 5–6 generations; and south of the Nanling Mountains, 6–8 generations. Altitude also influences the number of generations in the same area.
In southern regions, middle and small larvae overwinter in fields, ditches, ridges, canals, saplings, and bamboo groves. They become active when temperatures rise above 12°C. The first generation typically appears in *Zizania* (wild rice), while later generations mainly affect rice crops.
Each developmental stage has a specific temperature threshold: 12.6°C for eggs, 9.3°C for larvae, and 14.9°C for pupae. At 15–16°C, the egg stage lasts 15–16 days, while at 21–26°C, it takes only 5 days. The larval period is around 18–20 days at 26–28°C, but extends to 21 days if the temperature is below 24°C or above 30°C. Overwintering larvae can survive for up to 180 days. The pupal stage lasts 7–16 days, and adults live for 2–19 days.
Adults emerge overnight, usually in the early morning, and lay eggs shortly after. Newly hatched larvae first feed on the eggshell before climbing to the leaf tips. They feed on leaves and nodes, and during early morning or evening, they may drop into water. After irrigation, they move upward from the lower leaves. The final-instar larvae tend to disperse and pupate.
Environmental conditions such as low winter and spring temperatures or heavy rainfall in the previous month can increase the population of this pest.
To manage *Parnara guttata*, several methods can be used. One approach is manual removal of larvae through artificial techniques. Encouraging natural predators like parasitic wasps and dragonflies is also effective. If necessary, insecticides can be applied, such as 50% phoxim EC diluted 1500 times, 25% emulsifiable concentrate 1500 times, 2.5% chlorinated EC 2000 times, 10% imidacloprid WP 1500 times, or 35% SF 2 emulsion 1000 times. Each application should cover 70 liters of solution per 667 square meters, with treatments repeated every 10 days for 1–2 cycles.
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