Pseudaletia unipuncta (Haworth)

(Also known as Mythimna unipuncta (Haworth))

Taxonomic placing: Insecta, Holometabola, Lepidoptera, Noctuidae.

Common name: True armyworm.

Geographical distribution: North America, Hawaii, South America, the Mediterranean East Africa and the Sahel region, Central Asia. CIE map # 231, 1967. In the Middle East since the 1960’s.

Host plants: Mostly cultivated or wild cereals, such as wheat, barley, or maize. At high larval densities, also legumes that grow in or close to infested sites.

Morphology: The young larvae are pale green, turning dark when fully grown, up to 45-50 mm in length. A thin, broken white line is on their dorsum, and wide dark lateral stripes run along the body. Adults are light brown to pink, with a pale, pinhead-sized spot on each brown forewings (hence the specific name unipuncta). The hindwings are greyish.

Life cycle: All pest activities, flight, mating, oviposition and larval feeding, occur at night. Newly emerged females undergo a pre-oviposition period of two weeks, feeding on honeydew or nectar. They live for 2-3 weeks and may lay up to 2000 eggs, deposited in clusters of 25 to 150. The emerging larvae feed on succulent grasses. At high population density they may crawl in large groups from a depleted food source to another (hence “army worm”). When fully grown, they pupate in silk cocoons under leaf litter or in the soil. In the eastern Mediterranean the pest has 3-5 annual generations, but no winter diapause. Being strong fliers, they migrate in autumn from cold to warm regions in order to overwinter, flying back in the spring. The size of their populations fluctuates randomly from year to year.

Economic importance: The larvae, which are usually minor pests, may at times cause local damage. In the Mediterranean region of Turkey, damage to maize by P. unipuncta is increasing, as larvae cut through the tassels of unfertilized maize cobs. In the Azores, large pest infestations in summer and early autumn cause considerable damage, estimated at 8% (5 million EUR) of the annual vegetable production. Armyworms may invade grasses in wet areas, often after flooding. Damage to lawns can be extensive, leaving bare areas, especially when the pest occurs in nearby wheat and other small grains plots. The annual extent of the damage is inconsistent, due to the unpredictable nature of P. unipuncta outbreaks.

Management

Monitoring: Pheromone and black light traps are used for population monitoring. Field examinations are to be conducted at dawn or dusk, when the larvae are active.

Horticultural methods: Grass weeds, focal points of infestation, should be removed, and conventional tillage (which buries grassy stubble) in fields is to be preferred. Small grain crops should not, if possible, be grown adjacent to cereal fields.

Chemical control: Carbamates are sometimes used. Essential oils from plants of the families Apiaceae (also known as Umbelliferae) and Meliaceae, reduced pest numbers. If insecticidal treatments have to be used, they should be applied before the larvae reach their most destructive, last instar.

Biological control: Over 60 species of hymenopteous and dipterous parasitoids that occasionally reduce damage were recorded in North America. Their effect on the pest varies from time to time and from region to region. In addition, many beetles, ants and spiders, as well as birds, feed on the larvae. In the field the pest may be heavily attacked by a nuclear polyhedrosis virus and by entomopathogenic fungi. In the Azores entomopathogenic nematodes caused up to 60% pest mortality.

References

Akhtar, Y., Yeoung, Y.-R. and Isman, M.B. 2008. Comparative bioactivity of selected extracts from Meliaceae and some commercial botanical insecticides against two noctuid caterpillars, Trichoplusia ni and Pseudaletia unipuncta. Phytochemistry Reviews 7: 77–88.

Breeland, S. G. 1958. Biological studies on the armyworm, Pseudaletia unipuncta (Haworth), in Tennessee (Lepidoptera: Noctuidae). Journal of the Tennessee Academy of Science 18: 263–347.

Guppy, F. 1967. Insect parasites of the armyworm, Pseudaletia unipuncta (Lepidoptera: Noctuidae), with notes on species observed in Ontario. Canadian Entomologist. 99: 94–106.

Magnarelli, L.A. and Andreadis, T.G. 2004. An epizootic of nuclear polyhedrosis virus in armyworms (Pseudaletia unipuncta) in Connecticut. Northeastern Naturalist 11: 75-80.

Medeiros, J., Rosa, J.S, Tavares, J. and Simões, N. 2000. Susceptibility of Pseudaletia unipuncta (Lepidoptera: Noctuidae) to entomopathogenic nematodes (Rhabditia: Steinernemitidae and Heterorhabditidae) isolated in the Azores: effect of nematode strain and host age. Journal of Economic Entomology 93: 1403–1408.

Oliveira, L., Melo, R. and Tavares, J. 1999. Host age of Pseudaletia unipuncta (Lepidoptera: Noctuidae) and parasitic capacity of Glyptapanteles militaris (Hymenoptera: Braconidae). Environmental Entomology 28: 513-517.

Sousa, R.M., Rosa, J.S., Oliveira, L., Cunha, A. and Fernandes-Ferreira, M. 2013. Activities of Apiaceae essential oils against armyworm, Pseudaletia unipuncta (Lepidoptera: Noctuidae). Journal of Agriculture, Food and Chemistry 61: 7661-72.

Steinkraus, D. C., A. J. Mueller, and R. A. Humber. 1993. Furia virescens (Thaxter) Humber (Zygomycetes: Entomophthoraceae) infections in the armyworm, Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) in Arkansas with notes on other natural enemies. Journal of Entomological Science 28: 376–386.

Vieira, V., Oliveira, L., Garcia, P. and Tavares, J.. 2004. Assessment of Pseudaletia unipuncta (Haworth) (Lepidoptera: Noctuidae) populations in Azorean pastures by light and pheromone traps. Arquipélago. Life and Marine Sciences 21A: 33-42.

Yathom, s. 1966. Phenology of Pseudaletia (Cirphis) unipuncta (Haw.) Noctuidae, Lepidoptera in Israel. Israel Journal of Entomology 1: 55-61.

Websites: http://www.ipmimages.org/browse/subthumb.cfm?sub=58974 http://en.wikipedia.org/wiki/Mythimna_unipuncta