The armyworm is a significant pest that affects grassy plants across the globe, and it poses a threat to all provinces in China. The larvae of this pest are particularly complex, with a strong preference for grassy vegetation. Commonly affected pastures include ryegrass, Sudan grass, orchardgrass (Dactylis glomerata), green foxtail (Setaria viridis), as well as staple crops like wheat, corn, and rice. The larvae feed on the leaves, with the first and second instars causing small round holes by consuming only the leaf flesh. By the third instar, they create irregular notches, and by the fourth to sixth instars, they enter an overeating phase. In severe infestations, the entire foliage can be devoured, leaving only thin, light-colored stalks.
Adult armyworms measure 17 to 20 mm in length, with a pale grayish-brown body and wings spanning 30 to 45 mm. The forewings feature two yellowish circular spots near the front edge, with a larger spot on the outside and a small white dot below it. A black spot is located on either side of the white dot. Along the trailing edge of the wing tip, there's a slanted dark brown pattern. From the one-fourth mark of the leading edge to the one-third mark of the trailing edge, seven to nine black dots are arranged in an arc. The hind wings are gray-brown on the inside and brown on the outside.
The eggs are oval-shaped, approximately 0.6 mm in diameter, yellowish-white, and covered with an irregular network-like pattern on the surface.
The larvae go through six instars, with body lengths ranging from 17 to 20 mm initially, and reaching up to about 38 mm when mature. Their coloration varies significantly, typically ranging from green to yellow-brown. They have five vertical black and white stripes along their bodies, with brown to sepia-colored heads and light brown to black mouthparts.
At the end of the abdomen, there is a bent-outward spine, with two pairs of small, curved spines on each side.
In southern regions, the armyworm reproduces year-round, with 5 to 8 generations per year. The egg-laying period lasts 6 to 15 days for the first generation, and 3 to 6 days for subsequent ones. The larval stage lasts 14 to 28 days, the pupal stage 1 to 3 days, the adult emergence period 10 to 14 days, and the pre-spawning period 3 to 7 days. It takes between 40 to 50 days to complete one full life cycle.
Adults are nocturnal, becoming active at night to feed, mate, and lay eggs. 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, feeding on grass during the day and hiding under clods or in dense vegetation when disturbed. Mature larvae often burrow into the soil or hide among plant debris.
Control methods include using traps to capture moths. A mixture of sugar, wine, vinegar, and water in a 1:1:4:16 ratio, combined with 2.5% trichlorfon powder, can be used as bait. These traps should be placed in pots, with 2 to 3 pots per hectare, positioned 30 to 35 cm above the grass. The bait depth should be 3 to 3.5 cm. Moths are attracted at night, and the pots should be covered during the day. Dead moths should be removed daily, and the bait should be refreshed every 5 to 7 days for 16 to 20 days.
Egg collection involves placing grasses in the field. About 150 grasses per hectare are used, and those with eggs are collected and burned to prevent further infestation.
Chemical control relies on insecticides that are safe for humans, animals, and the environment, such as 40% New Nongbao EC diluted 800-1200 times, 25% Hong Chong suspension concentrate diluted 500-800 times, 30% Horse Emulsion diluted 1000-1500 times, 90% Wan-Ling wettable powder diluted 1500-2000 times, 20% Bangshui emulsion diluted 1000-1200 times, and 90% trichlorfon liquid diluted 1000-1500 times. After application, the forage remains safe for livestock and poultry after 15 to 20 days.
Light trapping is effective in open areas where there is minimal obstruction and electricity is available. "Frequency-vibration insecticidal lamps" can be used to attract adult armyworms. One lamp is installed for every 40 to 60 acres, turned on in the evening and off in the early morning.
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