Mythimna separata (Walker) - Oriental Armyworm
Systematic position.Class Insecta, order Lepidoptera, family Noctuidae, genus Mythimna.
Synonyms.Pseudaletia separata (Walker), Cirphis separata (Walker), Leucania separata (Walker).
Biological group.Polyphagous pests.
Morphology and biology.Size and coloration varies insignificantly. Sexual dimorphism is not expressed. Wing span is 38-48 mm. Forewings are grayish-yellow, with dark-gray or reddish-yellow tint. Round and reniform spots are light or yellowish with indistinct edges; reniform spot with white point at lower margin. External wing margin blackened obliquely from top backward, with dark stroke and with a row of dark points. Hindwings are gray, with dark external margin. Antennae are thread-like. Female fertility varies from 300 to 1600 eggs. Moth life span is about 2-3 weeks. Eggs are laid in 2-4 rows in groups of tens, on weed and cultural plants behind sheath of lower leaves, on radical leaves, stalks, and in cracks of bark or under bark of bush willows and dry stalks of wormwood. Development of eggs lasts 4-12 days depending on weather (temperature and humidity of air). Eggs have spherical form (0.5-0.6 mm in diameter), milky-white; their surface is thinly reticulate. Larvae usually have 6 instars (very seldom 7 instars), reaching 40 mm in length at older age. Larva with 2 wide black-brown and one intermediate light dorsal stripe, with black-brown lateral stripe along spiracle line; spiracles brown with black rim. Abdominal legs are underdeveloped on 1st and 2nd abdominal segments. Larvae pupate in soil at depths to 2 cm, under lumps of ground or under tussocks. Before pupation the larvae make soil caves at depths of 2 cm. The larvae usually pupate along edges and boundaries of fields or along edges of roads. Pupal phase lasts 13-21 days. Pupae are yellowish-brown, shiny. Body length is about 15-20 mm. It has a cremaster on last segment bearing 2 bent and crossed spines and 4 thin hooked setae. Overwintering usually occurs during stage of pupa in soil at a depth of 3-5 cm, but sometimes during larval or adult stage. Development of one generation lasts 25-45 days.
Distribution.It is distributed in China, Korea, Japan, Southeast Asia, Australia, Oceania, in the south of Uzbekistan. In Russia this noctuid moth is distributed in Primorskii Territory, in the south of Khabarovsk Territory, Amur Region, Sakhalin and Kurils.
Ecology.Polycyclic species, a pest in the territory between latitudes 45°N and 45°S and between longitudes 60°E and 170°W. In the Far East it develops in 2 generations. It is known as a migrant species, especially in the years of mass outbreaks; its larvae move in rows that are 15-20 m wide, searching food at night and in the afternoon, able to cross small rivers. Moths can migrate distances to 1500 km; the direction of migrations is connected to monsoon winds and air streams of cyclonic origin. It is a moisture loving and thermophilic species. The sum of degree-days for development of 2 generations equals 2200° at a threshold of 10°C. Optimum temperature is 23-30°C for larvae, 25°C for pupae, and 20-25°C for moths. Optimum relative air humidity is 80-95%. Moth flight of the overwintered generation occurs from the end of May until the 2nd third of June; moth flight of 1st generation in 1st-2nd thirds of August; moth flight of 2nd generation in September-October. Moths feed on nectar of flowers and aphid exudates on dandelion, vetch, bird cherry, yellow acacia, oak, poplar, maple, and on hazel (by exudates of young shoots). The noctuid development depends on temperature and precipitation, on presence or absence of snow cover during autumn-winter period, and upon conditions of larval feeding. Noctuid migrations, as well as activity of entomophages (predators and parasites) and entomopathogens, render an appreciable influence on the Oriental Armyworm number. Noctuid larvae are polyphages, preferring cereals; they populate plains (wheatgrass fallows, shorthear meadows) by rivers, lakes, or bogs, preferring false wheat, shorthear, chicken millet, and reed. Larvae of all instars feed mainly on leaves. The older larvae of 4-6 instars cause the main harm, roughly gnawing out and eating around leaf plate, and damaging inflorescences, ears, growth point, grain in ears. Starting with weeds, the larvae then pass to cultural plants. Larvae of 1st generation cause the greatest harm. In 2nd generation the harm is insignificant. Outbreaks of mass reproduction are rare, relating mainly to insect migrations. Local populations are depressed or they form local centers of high numbers.
Economic significance.The pest strongly damages oat, wheat, barley, winter rye, maize. It can injure soya, fodder grasses, less often it damages rice. Economic threshold of harmfulness (ETH) on agricultural lands as a whole is 10 larvae /sq.m. for the 1st noctuid generation, and 20 larvae /sq. m. for the 2nd generation. Control measures include weeding, interrow cultivations, removal of crop residues from fields after harvesting, deep autumn plowing, optimal dates of early sowing, cultivation of resistant varieties, insecticide treatments of crops, release of such entomophages as Trichogramma spp. Monitoring is possible with use of sex pheromone traps.
Related references:Berger, L.P. 1985a. Prediction of population dynamics of Mythimna separata in the Far East. In: Polyakov, I.Ya., ed. Automation principles of phytosanitary diagnostics. Proceedings of VIZR, issue 79, Leningrad: VIZR, p. 68-75 (in Russian).
Berger, L.P. 1985b. Substantiation of methods for the Oriental Armyworm occurrence and reproduction in the Far East. PhD Thesis, Leningrad - Pushkin: VIZR, 18 p. (in Russian).
Dolzhenko,V.I., ed. 2004. Methodical recommendations on registration tests of insecticides, acaricides , molluscocides and rodenticides in agriculture. Collective of authors. St.-Petersburg: VIZR, 363 p. (in Russian).
Kononenko, V.S. 1988. Noctuidae. In: Belyaev, E.A. et al., eds. Butterflies - pests of the Far Eastern agriculture and forestry. Keys. Vladivostok: DVO AN SSSR, p. 217-262 (in Russian).
Kononenko, V.S. 2003. Noctuidae. In: Ler P.A., ed. Keys to the insects of the Russian Far East. V. 5, issue 4. Trichoptera and Lepidoptera. Vladivostok: Dal.nauka, 688 p. (in Russian).
Li Xiu-zhen, Gong Pei-yu, Vu Kun-jun. 1992. Life tables of the armyworm, Mythimna separata (Walker) at different temperatures and its thermal requirement for development. Acta entomologica Sinica 35(4): 415 - 421 (in Chinese, with Engl. sum.).
Makarova, L.A & Doronina, G.M. 1988. Agrometeorological predictors for forecasting the reproduction of agricultural crop pests. Leningrad: Gidrometeoizdat, 214 p. (in Russian).
Makarova, L.A & Doronina, G.M. 1994. The synoptic approach to forecasting long-range migration of insect pests. St.- Petersburg: Gidrometeoizdat, 199 p. (in Russian).
Onisimova, Z.G., Kononenko, V.S., Belyaev, E.A., Tovba, M.S. 1987. The Oriental Armyworm - pest of grain crops. In: Leley, A.S., ed. Vladivostok: DVO AN SSSR, 82 p. (in Russian).
Pospelov, S.M. 1989. Noctuids - pests of agricultural crops. Moscow: Agropromizdat, 112 p. (in Russian).
Sharma, H.C., Sullivan, D.J. 2000. Screening for Plant Resistance to Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae) in Pearl Millet, Pennisetum glacum. J. Agric. Urban Entomol. 17(3): 125-134.
Sukhareva, I.L. 1999. Noctuidae. In: Kuznetsov, V.I., ed. Insects and mites - agricultural pests. V. 3, part 2. Lepidoptera. St.Petersburg: Nauka, p. 332-378 (in Russian).