Spodoptera littoralis (Boisduval)
Taxonomic placing: Insecta, Holometabola, Lepidoptera, Noctuidae
Common name:Egyptian cotton leaf worm.
Geographical distribution: Africa and countries in the Mediterranean region; CIE Map #232, 1967.
Host plants: Many commercial and wild plants.
Morphology: The forewings of the moth are brown, with many pale cream streaks and grey-blue overtones, more pronounced in the male, whereas the female has more brownish overtones. The hindwings are a translucent white, edged with brown, body length about 16 mm. The young larva is pale green, its color later varying from dark grey to reddish; with a brown head; when mature the body is 35-45 mm long. It bears large dotes with black hairs on each segment, and two large dorsal triangular markings on the 1st and 8th segments.
Life cycle: Adult emergence takes place at dusk and later, in the early part of the night. A female usually lays about 1000 eggs or more, even up to 3,500, in batches of 30-300. The eggs are covered with brownish-yellow hairs that protect the eggs from natural enemies. Most egg batches are placed on the lower parts of plants. Initially the larvae aggregate on the underside of leaves, dispersing later and remaining solitary for the rest of their development. They feed nocturnally, sheltering in the soil by day. Complete larval development can be as short as two weeks during mid-summer, up to 2-3 months in winter. Mature larvae crawl down into the soil, wherein they form a cocoon in which they pupate. During periods of high temperatures and low humidity the vulnerable neonate larvae suffer much mortality. The pest develops throughout the year, overwintering in the soil during cold spells without undergoing diapause. In the Middle East the leaf worm raises 7-10 annual generations. The moths live for 1-2 weeks and easily disperse by flying.
Economic importance: This leaf worm is a destructive pest in subtropical and tropical regions, infesting many edible and ornamental crops. It is a major pest of cotton, maize, tomato, tobacco and potatoes in the Eastern Mediterranean. Potentially it is also a pest of glasshouse crops and therefore regarded as a quarantine pest in the European Union. The young larvae feed on the foliage pf cotton, producing “windows” but leaving the upper epidermis layer intact. Large numbers of older larvae can defoliate plants and completely destroy crops, then move to adjacent fields and crops. Larval penetration into maturing cotton bolls auses considerable damage as well as introducing bacterial and fungal rot agents that cause secondary damage.
Monitoring: Traps baited with a sex pheromone.
Cultural control: In organic cotton production in Egypt, the pest is hand-collected and the egg masses destroyed.
Mass-trapping: Efforts are being made to reduce the populations by mass- trapping the males in pheromone traps baited a sex pheromone.
Transgenic control: An enzymatic inhibitor expressed in transgenic tobacco lines fed to S. littoralis larvae had no effect on their development, but reduced their fertility.
Chemical control: Many S. littoralis populations are resistant to pesticides and due to emerging cross resistance are difficult to control. Spinosad provided good control in Turkey. Pyrethroids are often used in greenhouses. Egyptian strains of Bacillus thuringiensis (Bt) were promising, as were commercial Bt formulations when supplemented with adjuvants. Together with neem they are potential components of IPM of this and other noctuid larvae.
Biological control: Egg and larval parasitoids and predators can reduce pest numbers, but may be hindered by the extensive use of chemicals. The internal larval parasitoid Microplitis rufiventris Kok (Braconidae) is usually found with the leafworm in the fields, but Its controlling effect is uneven. Larvae may be infected by, or acquire by ingesting, infectious polyhedra of a specific baculovirus, Spodoptera littoralis nuclear polyhedosis virus (Spli NPV), which causes mortality within 1-2 weeks. At high pest population density the disease can increase to epidemic proportions. Marginal baculovirus titers can result in latent infections, which may be exacerbated by stress factors (low temperatures, high population density or limited food resources). Attempts were made to prepare more virulent commercial virus formulations in order to provide higher and consistent infection rates. Several entomopathogenic nematodes (EPNs) were assayed against the pest in India.
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Alfazairy, A.A., El-Ahwany. A.M., Mohamed, E.A., Zaghloul, H.A. and El-Helow, E.R. 2013. Microbial control of the cotton leafworm Spodoptera littoralis (Boisd.) by Egyptian Bacillus thuringiensis isolates. Folia Microbiologia (Praha) 58: 155-62.
Atwa, A.A. 2014. Susceptibility of Spodoptera littoralis) (Boisd.) to treated entomopathogenic rhabdities, Heterorhabditis bacteriophora and Steinernema sp. by different pesticides. Journal of Biopesticides 6: 149-159.
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De Leo, F. and Gallerani, R. 2002. The mustard trypsin inhibitor 2 affects the fertility of Spodoptera littoralis larvae fed on transgenic plants. Insect Biochemistry and Molecular Biology 32: 489-496.
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Hegazi, E.M., Hammad, S.M., Altahtawy, M. and El‐Sawaf, S.K. 1973. Parasites of the larval stage of the cotton leaf‐worm Spodoptera littoralis (Boisd.) (Noctuidae, Lepidoptera) in Alexandria region. Journal of Applied Entomology 74: 332-336.
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Mosallanejad, H. and Smagghe, G. 2009. Biochemical mechanisms of methoxyfenozide resistance in the cotton leafworm Spodoptera littoralis. Pest Management Science 65: 732-736.
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