The armyworm is a major pest that affects grassy plants worldwide, and it causes damage in all provinces of China. The larvae are particularly complex in their development, with a strong preference for grasses. Commonly affected pastures include ryegrass, Sudan grass, orchardgrass (Dactylis glomerata), green foxtail (Setaria viridis), as well as crops like wheat, corn, and rice. The feeding behavior of the larvae changes as they grow: early instars (1st to 2nd) feed on leaf flesh, creating small round holes, while 3rd instar larvae cause irregular notches. By the 4th to 6th instars, the larvae enter an overeating phase, which can result in severe damage where entire leaves are consumed, leaving only thin stalks.
Adult armyworms measure between 17 mm and 20 mm in length, with a pale grayish-brown coloration. Their wingspan ranges from 30 mm to 45 mm. On the forewings, there are two yellowish round spots near the front edge, with a larger spot on the outside and a small white dot below it. A small black spot is located on either side of the white dot. A slanted dark brown pattern appears in the lower third of the wing’s trailing edge, while 7 to 9 black dots are arranged in an arc from one-quarter of the leading edge to one-third of the trailing edge. The hind wings are gray-brown on the inside and darker on the outside.
The eggs are oval-shaped, about 0.6 mm in diameter, and have a yellowish-white color with an irregular network-like pattern on the surface. The larvae go through six instars, reaching a maximum body length of around 38 mm. Their color varies significantly, ranging from green to yellow-brown, with five distinct vertical lines of black, white, and brown on the body. The head is brown to sepia, and the mouthparts are light brown with some black markings.
At the end of the abdomen, there is a small, bent-outward spine, and each side of the spine has two pairs of small, curved spines. Armyworms reproduce year-round in southern regions, completing 5 to 8 generations per year. The first egg-laying period lasts 6 to 15 days, while later generations take 3 to 6 days. The larval stage lasts 14 to 28 days, followed by a pupal stage of 1 to 3 days, then a 10 to 14-day adult emergence period. The pre-spawning period for adults lasts 3 to 7 days, and the full life cycle takes 40 to 50 days.
Adult moths are active at night, feeding, mating, and laying eggs in the evening. Each female can lay between 1,000 and 2,000 eggs. The larvae have six instars and exhibit a pseudo-dormant behavior. They are most active at night, hiding in grass during the day. Mature larvae often burrow into the soil or under clods of earth.
For control, one method involves using sugar-wine-vinegar traps mixed with 2.5% trichlorfon powder (in a ratio of 1:1:4:16). These traps are placed in pots, with 2 to 3 pots per hectare, positioned 30–35 cm above the grass. The lure depth should be 3–3.5 cm. Pots are covered during the day and opened in the evening. Dead moths are removed daily, and the lures are refreshed every 5–7 days for a total of 16–20 days.
Another approach is manually collecting eggs by placing grasses in the field. About 150 grasses per hectare are used, and those with eggs are collected and burned. Insecticides such as 40% New Nongbao EC (diluted 800–1200 times), 25% Hong Chong suspension concentrate (500–800 times), 30% Horse Emulsion (1000–1500 times), 90% Wan-Ling wettable powder (1500–2000 times), 20% Bangshui emulsion (1000–1200 times), and 90% trichlorfon liquid (1000–1500 times) are recommended. After treatment, the forage remains safe for livestock and poultry after 15–20 days.
In areas with open fields and good visibility, "frequency-vibration insecticidal lamps" can be used to attract and kill adult moths. One lamp is installed per 40–60 acres, turned on in the evening and off in the early morning. This method is effective for reducing moth populations and preventing further infestations.
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