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Spodoptera littoralis
Adult African cotton leafworm
Scientific classification
Kingdom:
Animalia
Phylum:
Arthropoda
Class:
Insecta
Order:
Lepidoptera
Family:
Noctuidae
Genus:
Spodoptera
Species:
S. littoralis
Binomial name
Spodoptera littoralis
(Boisduval, 1833)
Synonyms

Hadena littoralis Boisduval, 1833 Prodena littoralis Boisduval, 1833

The Spodoptera littoralis, also referred to as the African cotton leafworm or Egyptian cotton leafworm or Mediterranean Brocade, is a species of moth in the family Noctuidae. S. littoralis is found widely in Africa, Mediterranean Europe and Middle Eastern countries. It is a highly polyphagous organism that pests on many cultivated plants and crops.[1] As a result, this species was assigned the label of A2 quarantine pest by the EPPO and was cautioned as a highly invasive species in the United States.[2][3] The devastating impacts caused by these pests have led to developments of both biological and chemical control methods.[4]

Taxonomy[edit]

Egyptian cotton leafworm is one of the many species of genus Spodoptera and family Noctuidae. The family Noctuidae was named by a French zoologist, Pierre André Latreille, in 1809 and the genus Noctuidae was named by a French entomologist, Achille Guenée, in 1852. Many of the species of genus Spodoptera are known to be pest insects.[5] The species was named by Jean Baptiste Boisduval in 1833. Synonyms of S. littoralis include Hadena littoralis and Prodenia littoralis. Due to the similarities between many pest insects, there have been noted incidents of many species that are almost identical to S. littoralis. For example, Spodoptera litura or cotton leafworm is often confused with S. littoralis, since the larvae and adult stages of two species are near identical. However, Viette demonstrated that these are two different species, as S. litura was found to mostly reside in Asia, Australia, and the Pacific Islands.[4][6]

Description[edit]

Hind view of wings

The adult moth has a body size that ranges from 15-20mm and wingspan that ranges from 30-38mm. The species' forewings are grey-brown colored and has an ocellus that are constructed by white oblique lines. The hind wings are usually much paler and have grey-colored margins.[1][4]

Similar species[edit]

Spodoptera littoralis is often confused with Spodoptera litura due to identical larvae and adult physical appearances. The only known way of distinguishing two species is by comparing the genitalia. Specifically, ductus and ostium bursae are known to be the same length in S. littoralis females but different in S. litura females.[7] Similarly, it was reported that P. ornithogalli is an American representative of S. littoralis as forms of two species are extremely close and related. The main difference between these species is that P. ornithogalli is much darker in color and has sharper markings.[8]

Distribution[edit]

African cotton leafworm resides in most regions of Africa and Middle Eastern regions such as Israel, Syria and Turkey. This species is also found in Southern and Mediterranean Europe, mainly in Spain, France, Italy and Greece.[1] It was found that S. littoralis' natural range is limited in the northern regions of Europe due to climate changes. As 25°C is the optimal temperature for the species' reproductive potential, areas with lower winter temperatures or fluctuating temperatures showed limited species distribution.[4][9]

Habitat[edit]

S. littoralis resides in areas with infrequent winter frosts due to the species' sensitivity to fluctuating temperature. The adult moths disperse into different regions in Africa and Mediterranean Europe and reside in various plants, in which the females lay eggs and the larvae primarily grow.[4]

Food resources[edit]

Larvae[edit]

There are many reported plant species and families that S. littoralis larvae feeds on. Specifically, the range of host plants on which S. littoralis feeds covers over 40 different plant families and at least 87 different plant species. S. littoralis larvae prefer to feed on young leaves, young shoots, stalks, bolls, buds and fruits. Some of these host plants are also known to affect larval growth. For an example, whereas larvae that fed on castor oil leaves had shortened larval and pupal duration, those that fed on sweet potato leaves had prolonged larval and pupal duration.[10]

Adult[edit]

S. littoralis is reported to be polyphagous. Few of the economically important crops that are damaged by S. littoralis include Ipomoea batatas (sweet potato), Solanum lycopersicum (tomato), Zea mays (corn), Triticum aestivum (wheat) and etc. Some of the other plants/crops that are also damaged by this species include Capsicum (peppers), Chloris gayana (rhodes grass), Hibiscus mutabilis (cottonrose) and etc.[4]

Life cycle[edit]

Egg[edit]

Female moths lay a batch of eggs that ranges from 20-1000 eggs on the lower side of the host plant's leaves. After the eggs are laid, female coats the eggs with scales from its abdomen. These spherical eggs show white to yellowish color and are 0.6mm in diameter. These white-yellow color of the eggs turn black just before hatching due to the presence of black larval head near the transparent shell.[1][4]

Larvae[edit]

Spodoptera littoralis larvae

Larvae body length ranges from 40-45mm. The larvae is usually hairless and varies in color. It has been noted that new born larvae has grayish or dark-green body color whereas the developed larvae has brownish or yellowish body color. Dark and light longitudinal bands along with two dark semi-circular spots on the back are noted characteristics of the larvae. The newly hatched larvae up to third-instar mainly feed on the lower side of the leaves but the later instar larvae feed on both sides. S. littoralis larvae in general are known to feed in the dark. It also has been observed that larvae up to their third and fourth-instar usually remain in their host plant but fifth and sixth-instar larvae leave the host plant during the day and climb back up at night.[1][4]

Pupa[edit]

The pupa is around 20mm long and cylindrical in shape. Initially, the pupa is green colored with reddish abdomen but it turns reddish-brown within few hours. Pupation usually occurs 3-5cm deep in the solid ground under soil. The duration of pupation is around 5-6 hours.[1][4]

Adult[edit]

Adult moth has a greyish-brown body that is around 15-20mm long. The wingspan of the adult moth ranges from 30-38mm. The forewing of the adult moth has brownish color with paler veins whereas the hindwing is more lightly colored (greyish-white). There are also oblique white bands on the forewing.[4] The adult moth appears at night and live about 5-10 days.[11]

Predators[edit]

There are many known predators, pathogens and parasite species that control the growth and distribution of S. littoralis. Of the natural predators of S. littoralis, ladybirds have been noted to prey on young larvae and eggs. Other known generalist predators include Paedeus fuscipes(staphylinid rover beetle), Paederus alferii, Labidura riparia, Creontiades pallidus and so on. [4] Spiders are also known predators of this species. Specifically, Cheiracanthium mildei and Ummeliata insecticeps are known dominant predator species of S. littoralis that not only feed on the larvae but also induce dispersion from host plant.[12]

Mating[edit]

Female/male interaction[edit]

Most adult moths mate on the day that they emerge from pupa. Duration of copulation ranges from 20 minutes to 2 hours. Studies revealed that age difference between the male and female moth is crucial in determining reproductive capacity, adult lifespan and egg quality.[4] The most effective age difference that increased egg fertility was 4 days difference between the male and female. When a 4-day old male mated with a fresh born female, egg fertility was observed to be high. However, females laid most eggs when it mated with a male who was one day older.[13]

Pheromones[edit]

The pheromone secreted by females for mate calling is (Z,E)-9,11-tetradecadienyl acetate. As most matings occur at night, females producing largest amount of pheromone was observed 2-3 hours into scotophase, a dark phase of light cycle. The amount of pheromone in these females ranged from 6-8 ng. Lowest amount of pheromone was excreted few hours before the dark phase ended.[14] Other than its function to attract mates, female-produced pheromones may also synchronize male circadian rhythm.[15]

Courting[edit]

Antennae serves an important function in adult moth courtship. A male answering a female mate-call fully extends its antennae while flying over the female. A sign of rejection in females is noted by rapid wing flicks, whereas lifted wings, curved abdomen and withdrawal of pheromone in females are signs of female's acceptance for copulation. Once male and female are attached during copulation, male move its head downwards. Males without antennae did not answer female mate-call, which resulted in lack of mating. Females without antennae seldom mated but all matings were reported to be abnormal.[16]

Interaction with humans[edit]

Pest of crop plants[edit]

Because of S. littoralis' polyphagous behavior, the species has been damaging to many economically crucial crops such as cotton, tomato, maize and various other vegetables. Most of the damages are a direct result of extensive larvae feeding. Often times, larvae will either create large holes in the leaves, only leaving the big veins of the leaves or bear into the bud for consumption.[17] Most of the plants or vegetables that are attacked by S. littoralis are unsuitable for consumption as the damages are too severe. Of different types of host plants, cotton has been one of the main targets of S. littoralis. The species feed on cotton leaves, flower buds, fruiting points, and bolls, leaving the plant unsuitable for any further usage. Such damage of cotton plant is most prevalent in North Africa, especially in Egypt.[4] As a result, EPPO has assigned S. littoralis as A2 quarantine pest.[2] In the United States, S. littoralis has been listed as an exotic organism with high invasive risk.[3] Since 2004, there were 65 reported incidents of S. littoralis entrance that were at the U.S. ports of entry.[18]

Prevention and control[edit]

Due to S. littoralis' devastating effect on crops, numerous attempts have been made to counteract the species' dispersion and activities. These preventative methods are mainly divided into biological and chemical methods. Biological methods include using parasitoids or predators to control moth reproduction and dispersion.[4] Usage of bacteria such as Bacillus thuringiensis in combination with bacterial endochitinase has also been utilized recently to control many bacteria-resistant strains of S. littoralis larvae. Studies revealed that the synergistic toxic effect of Bacillus thuringiensis and bacterial endochitinase successfully resulted in reduced larval weight.[19] However, direct usage of these biological methods are yet not legal.[4] Similarly, chemical insecticides including organophosphorus, synthetic pyrethroids have been widely used to control S. littoralis.[4] Recent studies also revealed that insect growth regulators such as azadirachtin from neem tree are effective in controlling S. littoralis larvae as azadirachtin-treated larvae had overall higher mortality rate as well as reduced growth rate due to increased deformity and growth disruption.[20]

References[edit]

  1. ^ a b c d e f Noma, T; Colunga-Garcia, M; Brewer, M; Landis, J; Gooch, A. "Egyptian cottonworm: Spodoptera littoralis" (PDF). ipm.msu.edu. Michigan State University.
  2. ^ a b OEPP/EPPO (2015). "Diagnostic protocol for Spodoptera littoralis, Spodoptera litura, Spodoptera frugiperda, Spodoptera eridania". Bulletin OEPP/EPPO Bulletin. 34: 257–270.
  3. ^ a b USDA-APHIS (2008). "Pests of national concern for fiscal year 2009". {{cite journal}}: Cite journal requires |journal= (help)
  4. ^ a b c d e f g h i j k l m n o p "Spodoptera littoralis (cotton leafworm)". CABI. Retrieved 11 October 2017.
  5. ^ Meagher, Robert (2008). "MONITORING FOR EXOTIC SPODOPTERA SPECIES (LEPIDOPTERA: NOCTUIDAE) IN FLORIDA". USDA-ARS Center for Medical, Agricultural and Veterinary Entomology: 517–522.
  6. ^ Viette, Pierre (1962). "Nouvelles espèces malgaches de Noctuelles Quadrifides (Lépidoptères)". Bulletin de l'Académie malgache: 1–825.
  7. ^ "Spodoptera litura (taro caterpillar)". CABI. Retrieved 11 October 2017.
  8. ^ Transactions of the Entomological Society of London (vol 38 ed.). Royal Entomological Society of London. 1890.
  9. ^ Sidibe, B; Lauge, G (1977). "Effect of warm periods and of constant temperatures on some biological criteria in Spodoptera littoralis Boisduval (Lepidoptera Noctuidae)". Annales de la Societe Entomologique de France. 13: 369–379.
  10. ^ Salama, H; Dimetry, N; Salem, S (1971). "On the Host Preference and Biology of the Cotton Leaf Worm Spodoptera littoralis Bois". Zeitschrift für Angewandte Entomologie. 67 (1–4): 261–266.
  11. ^ Salama, H; Shoukry, A (1972). "Flight range of the moth of the cotton leaf worm Spodoptera littoralis (Bois.)". Zeitschrift fur Angewandte Entomologie. 2: 181–184.
  12. ^ Mansour, Fadel; Rosen, David; Shulov, A (1981). "Disturbing effect of a spider on larval aggregations of Spodoptera littoralis". Entomologia Experimentalis et Applicata. 29 (2): 234–237.
  13. ^ Nasr, E.S.A.; Nassif, F.M. (1978). "Effect of age of the adult stage of the cotton leaf worm, Spodoptera littoralis (Boisd.), on the rate of oviposition, egg-fertility and life span of moths (Lepidoptera: Noctuidae)". Bulletin de la Societe Entomologique d' Egypte. 59: 289–294.
  14. ^ Dunkelblum, E; Kehat, M; Harel, M; Gordon, D (1987). "Sexual behaviour and pheromone titre of the Spodoptera littoralis female moth". Entomologia Experimentalis et Applicata. 44 (3): 241–247.
  15. ^ Silvegren, Germund; Löfstedt, Christer; Rosén, Wen Qi (2005). "Circadian mating activity and effect of pheromone pre-exposure on pheromone response rhythms in the moth Spodoptera littoralis". Journal of Insect Physiology. 51 (3): 277–286.
  16. ^ Ellis, Peggy; Brimacombe, Linda (1980). "The mating behaviour of the egyptian cotton leafworm moth, spodoptera littoralis (Boisd.)". Animal Behaviour. 28 (4): 1239–1248.
  17. ^ Bishara, I (1934). "The cotton worm Prodenia litura F. in Egypt". Bulletin de la Société Entomologique d'Egypte. 18: 223–404.
  18. ^ Ellis, S (2004). "New Pest Response Guidelines: Spodoptera". USDA/APHIS/PPQ/PDMP.
  19. ^ Regev, A; Keller, M; Zilberstein, A (1996). "Synergistic activity of a Bacillus thuringiensis delta-endotoxin and a bacterial endochitinase against Spodoptera littoralis larvae". Appl. Environ. Microbiol. 62: 3581–3586.
  20. ^ Martinez, S; van Emden, H (2001). "Growth disruption, abnormalities and mortality of Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) caused by Azadirachtin". 30. {{cite journal}}: Cite journal requires |journal= (help)

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