Rice Ridged Rice Butterfly
The scientific name *Parnara guttata* Bremer et Grey belongs to the order Lepidoptera, family Heteroidea. It is commonly known as the rice moth, or sometimes referred to as the rice worm. While it is not reported in Xinjiang and Ningxia, it is widely distributed throughout China.
This pest primarily attacks a variety of crops including rice, millet, corn, sorghum, barley, wheat, bamboo, reeds, white wax trees, alfalfa, and setaria. The larvae are particularly destructive. After hatching, they climb to the edges or tips of leaves, where they roll them into cylindrical shapes, creating a protective shelter that can cause significant damage to the host plant.
Morphologically, the adult moth has a body length of 17–19 mm and a wingspan of 28–40 mm. Its body and wings are dark brown with a slight greenish tint on the head and thorax. The front wings feature 7–8 translucent white spots arranged in a semi-circular pattern, with one larger spot at the bottom. The hind wings have four transparent white spots aligned in a straight or nearly straight line. The eggs are brown, hemispherical, measuring about 0.9 mm in diameter, initially gray-green, later turning pinkish. Each egg has 8–12 petal-like structures on the top.
The final instar larvae are 27–28 mm long, with a brownish-yellow head featuring a distinct "mountain"-shaped brown mark. Their bodies are yellow-green with a dark green dorsal stripe and a brownish patch. The pupae are light yellow, cylindrical, and approximately 22–25 mm long, with a flat tip.
In terms of life cycle, the number of generations varies by region: two generations north of the Great Wall, three generations north of the Yellow River, four to five generations south of the Yangtze River, five to six generations south of the Nanling Mountains, and up to six to eight generations in southern regions. Altitude also affects the number of generations. In the south, middle- and small-sized larvae overwinter in fields such as ridges, ditches, and bamboo groves. They become active when temperatures exceed 12°C.
The first generation typically appears in *Zizania* (wild rice), while later generations mainly feed on rice. The development thresholds for each stage are around 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 26°C, it takes only 5 days. Larval development at 26–28°C takes 18–20 days, but it 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 begin laying eggs. Newly hatched larvae first feed on the eggshell before moving to leaf tips, where they feed on leaves and nodes. They tend to crawl out during early morning or evening hours and fall into water. After irrigation, they move upward from the lower leaves. The final instar larvae are more likely to disperse and pupate. In colder winters or after heavy rainfall, their population tends to increase.
For control, several methods can be employed. One approach is manual removal of larvae. Encouraging natural predators like parasitic wasps and dragonflies can also help. If necessary, insecticides such as 50% phoxim EC diluted 1500 times, 25% emulsifiable concentrate (EKC) diluted 1500 times, 2.5% chlorpyrifos EC diluted 2000 times, 10% imidacloprid WP diluted 1500 times, or 35% suspension concentrate (SF) 2 Emulsion diluted 1000 times can be applied. Spraying 70 liters per 667 square meters, once every 10 days, and repeating 1–2 times can effectively manage infestations.
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