Armyworm
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**Mythimna separata (Walker), commonly known as the armyworm, is a species of moth belonging to the family Noctuidae. It is also referred to by several synonyms, including Leucania separata Walker. This pest is widely recognized under various common names such as the multicolored caterpillar, wheat silkworm, and razor worm. Its distribution spans across most regions of China, except for Xinjiang, where it has not been reported.**
**The armyworm primarily feeds on cereal crops such as wheat, rice, millet, and corn, but it is also polyphagous, attacking over 104 plant species from 16 different families, including cotton, legumes, and vegetables. The larvae are highly destructive, consuming leaves rapidly and, in severe infestations, can strip entire fields of foliage, leading to significant yield losses. Due to its migratory behavior, omnivorous feeding habits, and high reproductive capacity, this pest is considered one of the most important agricultural threats in China.**
**Morphologically, adult armyworms have a body length of 15–17 mm and a wingspan of 36–40 mm. Their head and thorax are beige, while the abdomen is dark brown. The forewings vary in color, ranging from brownish-yellow to orange, with distinct patterns that include a few black spots along the inner margin, a kidney-shaped marking with a white dot at the back, and a series of black dots along the outer edge. The hind wings are dark brown, fading toward the base. The eggs are small, hemispherical, and shiny, usually laid in clusters on the tips of leaves or within leaf folds. Mature larvae can grow up to 38 mm long, with a reddish-brown head featuring a reticulate pattern and thick vertical lines on either side. The body color varies significantly depending on environmental conditions and food sources.**
**During outbreaks, the larvae may appear black on their backs, with a lighter ventral surface and a white mid-dorsal line. A faint blue hue may appear between the submarginal and medial lines, while the lateral lines range from pink to grayish-white. A wide dark band runs along the outer edge of the body, and the tip of the foot has a semi-circular dark spot. The larvae possess spines on their abdominal segments, with four spines per segment, two of which are thicker and slightly curved.**
**The life cycle of Mythimna separata varies by region, with 2–3 generations in the northeast and 6–8 generations in southern China. In colder areas north of 33°N latitude, the insect cannot overwinter, while in southern regions like Hunan, Jiangxi, and Zhejiang, larvae and pupae survive through winter in crop residues or weeds. Adults are nocturnal, emerging at dusk to feed and lay eggs at night. They prefer sweet and sour substances and are attracted to yellow dry leaves. Eggs are typically laid in clusters on the upper parts of leaves, especially in wheat and rice fields. Newly hatched larvae are gregarious and feed on the upper leaf surfaces, progressing to more aggressive feeding as they mature.**
**Optimal development occurs at temperatures between 10–25°C and humidity levels of 85%. Spawning is most active at 19–22°C and 90% humidity. High temperatures above 35°C inhibit egg-laying, while low humidity reduces larval survival. Adult moths require nectar for energy, and fields with abundant nectar sources tend to see higher egg production. Larvae thrive in densely planted, well-fertilized, and well-irrigated fields. Natural enemies include birds, frogs, parasitic wasps, and flies, which help regulate populations naturally.**
**Control methods include trapping adults using bait such as sweet vinegar pots, black lights, or straw traps placed in fields. Chemical control is recommended before the third instar, using insecticides like trichlorfon or malathion. Hormone-based pesticides such as diflubenzuron are also effective. Herbicides like phoxim, carbofuran, and amitraz can be used alone or in combination for better efficacy. Integrated pest management strategies, including biological control and cultural practices, are essential for sustainable control of this widespread and damaging pest.**