Spodoptera litura, otherwise known as the tobacco cutworm or cotton leafworm, is a nocturnal moth in the family Noctuidae. S. litura is a serious polyphagous pest in Asia, Oceania, and the Indian subcontinent that was first described by Johan Christian Fabricius in 1775.[1] Its common names reference two of the most frequent host plants of the moth. In total, 87 species of host plants that are infested by S. litura are of economic importance.[2] The species parasitize the plants through the larvae vigorous eating patterns, oftentimes leaving the leaves completely destroyed. The moth's effects are quite disastrous, destroying economically important agricultural crops and decreasing yield in some plants completely.[3] Their potential impact on the many different cultivated crops, and subsequently the local agricultural economy, has led to serious efforts to control the pests.[4]
S. litura is often confused with its close relative, Spodoptera littoralis. These two species are hard to discriminate between because the larvae and adult forms are identical. Inspecting the genitalia is the most certain way to tell the two species apart.[5]
Description
Sex differences
Morphology
There are slight but obvious differences in morphology between males and females of S. litura that allow for the easy differentiation of the two sexes. Male forewing length is 14–17 millimetres (1⁄2–5⁄8in) while female forewing length is slightly larger and measures 15–18 millimetres (5⁄8–3⁄4in). The orbicular spot on the forewing is also more pronounced in the males.[6]
Female
Male
Differences in food regulation
Regulation of macro nutrient input differs between males and females. Experimental results show that when S. litura are presented with two nutritionally complementary diet options, one rich in protein and a second rich in carbohydrates, females tend to consume more protein than males while no differences in carbohydrates exist. Body utilization of the macro nutrients differed as well. Females were very efficient at converting the protein consumed into body growth and mass, reflecting the bodily requirements to produce eggs. Males, on the other hand, were more efficient at depositing lipid from ingested carbohydrates. This fits in well with the migration patterns associated with mating. Males usually go out to find females during mating season, so the lipid deposits are thought to be energy reserves that will help the males in preparation for the migration.[7]
Similar species
Spodoptera litura and Spodoptera littoralis are very closely related species. Discriminating between the two species can be difficult because the larvae and adult forms look identical. In fact, these two species are so similar that previous records that have claimed the presence of S. litura in areas such as Russia, Germany, and the UK may actually have been referring to S. littoralis.[5] Since both species are polyphagous, taking note of the host plant is not helpful in correct identification.[8] The only way to properly differentiate between the two is by inspecting their genitalia. In S. littoralis, the ductus and ostium bursae are the same lengths while in S. litura, they are of different lengths. In males, the juxta have characteristic shapes for each species.[5]
Spodoptera littoralis
Spodoptera litura
Range
S. litura is the most common in South Asia.[9] However, its natural range extends from the Oriental and Australasian areas to parts of the Palearctic region as well.[6] The countries with the most widespread population of S. litura include but are not limited to China, Indonesia, India, Japan, and Malaysia.[2] The range of S. litura has also extended into non-indigenous regions through international trade. Moths in their egg, larvae, or pupae stages can be present in the soil, flower, or vegetation that are being transported across various regions. Pupae especially can be moved long distances, provided that they are not crushed, because of the relatively long pupation period.[5]
Habitat
S. litura is a general herbivore and takes residence on various plants.[10] The lower and upper limits of habitable temperatures are 10 and 37°C (50 and 99°F), respectively. Therefore, it is well suited for tropical and temperate climate regions.[5] As caterpillars, S. litura can only move short distances. However, adult moths can fly up to a distance of 1.5 kilometres (0.93mi) for a total duration of 4 hours. This helps disperse the moths into new habitats and onto different host plants as food sources are depleted.[5]
Although the length of a life cycle varies slightly throughout the different regions, a typical S. litura will complete 12 generations every year. Each generation lasts about a month, but temperature causes slight variations: life cycles in the winter tend to be slightly more than one month, and life cycles in the summer tend to be less than a full month.[5]
Egg
Eggs are spherical and slightly flattened. Each individual egg is around 0.6mm in diameter with an orange-brown or pink color. These eggs are laid on the surface of leaves in big batches, with each cluster usually containing several hundred eggs. Females have a typical fecundity of 2000 to 2600 eggs.[5] However, experiments have shown that high temperatures and low humidity are inversely related to fecundity.[2] When laid, the egg batches are covered with hair scales provided by the female, which gives off a golden brown color. Egg masses are 4–7 millimetres (5⁄32–35⁄128in) in total diameter, and eggs will hatch 2–3 days after being laid.[5]
Eggs
Larva
Larvae body length ranges from 2.3 millimetres (23⁄256in) to 32 millimetres (1+1⁄4in). The larva is variable in color based on age. Younger larvae tend to be a lighter green while older ones develop to a dark green or brown color. A bright yellow stripe along the dorsal surface is a characteristic feature of the larvae. The larvae also have no hair. Newly hatched larvae can be found by looking for scratch marks on leaf surfaces. Since S. litura is nocturnal, the larvae feed at night. During the day, they can usually be found in the soil around the plant. There are six instar stages, and by the last stage, the final instar can weigh up to 800mg.[5]
Newly hatched 1st instar larva
Pupa
Pupation lasts around 7 to 10 days and takes place on the soil near the base of the plant. The pupa is typically 15–20 millimetres (19⁄32–25⁄32in) long, and its color is red-brown.[5] A characteristic feature is the presence of two small spines at the tip of the abdomen that are about 0.5 millimetres (5⁄256in) long each.[6]
Adult
Adult moths are on average 15–20 millimetres (19⁄32–25⁄32in) long and have a total wingspan of 30–38 millimetres (1+3⁄16–1+1⁄2in). The body is a gray-brown color. The forewings are patterned with dark gray, red, and brown colors. The hindwings are grayish-white with a gray outline.[5] The mean female longevity is 8.3 days while for males it is 10.4 days.[11]
Male
Mating
There is no mating activity on the first night that the moth emerges.[11] The second night, however, accounts for about 70% of the matings.[1] This night marks the maximum activity. Females mate an average of 3.1 times while the males have a mating average of 10.3. During copulation, males transfer a mean of 1,052,640 sperm per mating.[11] Eggs during mating are laid in a cluster covered with hair from the female's abdomen. This acts as a protective layer from parasites predating on eggs.[12] Since S. litura is a nocturnal moth, all reproductive activities occur during the scotophase (dark phase). These reproductive activities include calling, courtship, mating, and oviposition. Several studies have pointed out that the female lifespan decreases after mating. The reasons for this are still not fully known. Several possible explanations include physical injuries from the male genitalia or the male accessory gland secretions that force females to commit more resources to reproduction instead of on herself.[1]
Male accessory glands
Male accessory glands (MAGs) are a reproductive evolutionary strategy adopted by males to gain higher fertilization. MAGs contain many different kinds of molecules including carbohydrates, lipids, and proteins. When MAGs are transferred from the male to the female during copulation, it exerts a wide range of effects on female post-mating behavior. One of these effects include suppressing female receptivity to future matings by reducing their sexual receptivity or sexual attractiveness. Experiments have shown that females exposed to MAGs do not engage in mating call behavior the night they are exposed to the secretion. A successful mating that resulted in fertilized eggs led to an even longer break from sexual receptivity.[1]
Mating also has an effect on stimulating egg production and ovulation. This phenomenon may also be a result of the mechanical stimulation of male genitalia during copulation. However, studies have shown that MAG secretions are necessary for the maximum stimulation of the eggs. As a result, female longevity is negatively correlated with the number of eggs laid because a large portion of resources end up being used for the development of eggs instead of on herself.[1]
Pheromones
In sexually reproductive animals, recognition and attraction of potential mates can occur in the form of pheromones.[13] In moth species, pheromones are produced by the females by pheromone glands and are released to attract males of their own species.[14] Accurate recognition of compatible mates is essential for reproductive success because failure to do so will come with steep costs: wasted time and energy, higher risk of predation, and reduction of viable offspring. Therefore, there is a strong selection for correct mate recognition signals that maximize reproductive fitness. Both S. litura and S. littoralis share the same 11 components that make up their pheromones (in different amounts), with (Z,E)-9,11-tetradecadienyl acetate (Z9,E11–14:Ac) acting as the major component.[13]
There is an inverse relationship between pheromone concentration within the bodies of females and the calling behavior of a female. This is because pheromones are released during female calling. It has been previously stated that the male accessory gland suppresses female calling and subsequently, re-mating. With calling suppressed, pheromone concentration builds up in the body of mated females. Therefore, when pheromone glands are analyzed, mated females will have a higher titre than virgin females. It is important to note that this result is different from previous studies on other insect species.[14]
Circadian rhythm
The circadian rhythm also affects pheromone release. It has been found that higher amounts of pheromones are released during scotophase (dark period) and that lower levels are released during photophase (light period). This pattern is thought to coincide with male flight patterns, which would maximize responsiveness to the pheromone signals being sent.[14]
Heterospecific matings
Heterospecific matings can be expected for phylogenetically closely related species with adjacent distribution, as is the case for S. litura and S. littoralis. Overlap in pheromone composition as discussed above also contributes to the lack of total reproductive isolation between the two species. Previous experiments have already shown that mating reduces the lifespan of female S. litura. This lifespan decreases even further when mating with a heterospecific S. littoralis male. It has also been shown that females lay significantly more eggs after a conspecific mating rather than after a heterospecific mating. Therefore, there is an evolutionary benefit to recognizing and mating with a mate of the same species.[13]
Predators
So far there are a reported 131 species of natural enemies that prey on S. litura at different points in their life cycle. These include different species of parasites that specifically target either the egg, larval, or pupal stage. There are also 36 species of insect and 12 species of spider that are known to be natural predators to the moths. The identity of these predators vary depending on the region being studied. Additionally, infections from fungi and viruses have been observed. The most commonly reported viruses are nuclear polyhedrosis viruses and granulosis viruses.[5] For example, in Karnataka, a granulosis virus was found in dead S. litura larvae. In this study, both eggs and larvae were susceptible, and the mortality rate ranged from 50% to 100% depending on the stage of the larvae. The older larvae were killed more rapidly than the younger larvae.[5]
Chemical signals
There are many ways the predators can locate its prey. One way is the release of chemical cues from the larvae that can act as a locator for predators searching for prey. The stink bug Eocanthecona furcellata is a predator that uses these types of chemical signals to locate and attain prey. Its prey locating behavior is activated when exposed to two chemical compounds released by S. litura larvae.[15]
Host plants
S. litura has over 112 host species belonging to over 40 plant families, making the species highly polyphagous.[9]S. litura cause severe damage to their hosts by their vicious eating habits as larvae. Some common host plants include but are not limited to: tobacco, cotton, soybean, beet, cabbage, and chickpeas.[3] When the host plant in a particular area is depleted, big groups of larvae will migrate to find a new food source.[5]
Interaction with humans
Pest activity
Some external signs of pest activity that can be seen are large holes on leaves, injured stem bases, and discoloration of leaves.[8] Because S. litura acts as a pest on many different kinds of agricultural crops, its presence can cause economic losses in regions where these crops are cultivated. For example, S. litura has been responsible for the 71% yield loss of groundnut in the southern states of India.[3] Another figure shows that S. litura can decrease tobacco yield by 23–50%. This can cause major economic strain since 36 million people are directly or indirectly involved in the production, sale, marketing, or transport of the tobacco crop. The significant impact on agriculture S. litura can have as pests has earned the species a spot on the quarantine list for many countries including the United States of America.[8]
Pesticides
Due to its presence in many important crops in agriculture, pesticides are always being applied on the species throughout the year. This has caused the rapid evolution of pesticide and insecticide resistance in S. litura.[9] In addition, the sheer amount of pesticides being used have caused concern for pesticide residue on food, environmental damage, and the destruction of beneficial species. Therefore, recent research studies have focused on other biological ways to effectively control these pests.[4] A current study of controlling this pest focuses on using the fungus Nomuraea rileyi on the larval stage of this moth. It was found that spraying a solution of this fungus on larvae in a laboratory setting has led to effective control of the late second and early third instar stages of the larvae on castor crops. When tested in the field, there was a very high larvae mortality of 88–97% 19 days after application of the fungal solution.[16]
1 2 3 Ahmad, Munir; Saleem, Mushtaq Ahmed; Sayyed, Ali H (2009-03-01). "Efficacy of insecticide mixtures against pyrethroid- and organophosphate-resistant populations of Spodoptera litura (Lepidoptera: Noctuidae)". Pest Management Science. 65 (3): 266–274. doi:10.1002/ps.1681. ISSN1526-4998. PMID19051214.
↑ Fukuda, T.; Wakamura, S.; Arakaki, N.; Yamagishi, K. (April 2004). "Parasitism, development and adult longevity of the egg parasitoid Telenomus nawai (Hymenoptera: Scelionidae) on the eggs of Spodoptera litura (Lepidoptera: Noctuidae)". Bulletin of Entomological Research. 97 (2): 185–190. doi:10.1017/S0007485307004841. ISSN1475-2670. PMID17411481. S2CID24593677.
1 2 3 Lu, Qin; Huang, Ling-Yan; Liu, Fang-Tao; Wang, Xia-Fei; Chen, Peng; Xu, Jin; Deng, Jian-Yu; Ye, Hui (2017-06-01). "Sex pheromone titre in the glands of Spodoptera litura females: circadian rhythm and the effects of age and mating". Physiological Entomology. 42 (2): 156–162. doi:10.1111/phen.12185. ISSN1365-3032. S2CID89807432.
↑ Yasuda, Tetsuya (1997-03-01). "Chemical cues from Spodoptera litura larvae elicit prey-locating behavior by the predatory stink bug, Eocanthecona furcellata". Entomologia Experimentalis et Applicata. 82 (3): 349–354. doi:10.1046/j.1570-7458.1997.00149.x. ISSN1570-7458. S2CID84406457.
↑ Devi, P. S. Vimala (1994). "Conidia Production of the Entomopathogenic Fungus Nomuraea rileyi and Its Evaluation for Control of Spodoptera litura (Fab) on Ricinus communis". Journal of Invertebrate Pathology. 63 (2): 145–150. doi:10.1006/jipa.1994.1028.
Helicoverpa zea, commonly known as the corn earworm, is a species in the family Noctuidae. The larva of the moth Helicoverpa zea is a major agricultural pest. Since it is polyphagous during the larval stage, the species has been given many different common names, including the cotton bollworm and the tomato fruitworm. It also consumes a wide variety of other crops.
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The cabbage looper is a medium-sized moth in the family Noctuidae, a family commonly referred to as owlet moths. Its common name comes from its preferred host plants and distinctive crawling behavior. Cruciferous vegetables, such as cabbage, bok choy, and broccoli, are its main host plant; hence, the reference to cabbage in its common name. The larva is called a looper because it arches its back into a loop when it crawls.
The African armyworm, also called okalombo, kommandowurm, or nutgrass armyworm, is a species of moth of the family Noctuidae. The larvae often exhibit marching behavior when traveling to feeding sites, leading to the common name "armyworm". The caterpillars exhibit density-dependent polyphenism where larvae raised in isolation are green, while those raised in groups are black. These phases are termed solitaria and gregaria, respectively. Gregaria caterpillars are considered very deleterious pests, capable of destroying entire crops in a matter of weeks. The larvae feed on all types of grasses, early stages of cereal crops, sugarcane, and occasionally on coconut. The solitaria caterpillars are less active and undergo much slower development. The species is commonly found in Africa, but can also be seen in Yemen, some Pacific islands, and parts of Australia. African armyworm outbreaks tend to be devastating for farmland and pasture in these areas, with the highest-density outbreaks occurring during the rainy season after periods of prolonged drought. During the long dry seasons ("off-season"), the population densities are very low and no outbreaks are seen.
The diamondback moth, sometimes called the cabbage moth, is a moth species of the family Plutellidae and genus Plutella. The small, grayish-brown moth sometimes has a cream-colored band that forms a diamond along its back. The species may have originated in Europe, South Africa, or the Mediterranean region, but it has now spread worldwide.
The Mediterranean flour moth or mill moth is a moth of the family Pyralidae. It is a common pest of cereal grains, especially flour. This moth is found throughout the world, especially in countries with temperate climates. It prefers warm temperatures for more rapid development, but it can survive a wide range of temperatures.
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Agrotis ipsilon, the dark sword-grass, black cutworm, greasy cutworm, floodplain cutworm or ipsilon dart, is a small noctuid moth found worldwide. The moth gets its scientific name from black markings on its forewings shaped like the letter "Y" or the Greek letter upsilon. The larvae are known as "cutworms" because they cut plants and other crops. The larvae are serious agricultural pests and feed on nearly all varieties of vegetables and many important grains.
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 is a pest of many cultivated plants and crops. 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. The devastating impacts caused by these pests have led to the development of both biological and chemical control methods. This moth is often confused with Spodoptera litura.
Mythimna unipuncta, the true armyworm moth, white-speck moth, common armyworm or rice armyworm, is a nocturnal agricultural pest belonging to the family Noctuidae. This moth is also commonly referred to by the scientific name Pseudaletia unipuncta. The species was first described by Adrian Hardy Haworth in 1809. Mythimna unipuncta is found in the Americas and in parts of Europe, Africa and Asia. Its original distribution is North and South America. It has been introduced to other places from there. They are known as armyworms because the caterpillars move in lines as a massive group, like an army, from field to field, damaging crops.
Helicoverpa punctigera, the native budworm, Australian bollworm or Chloridea marmada, is a species of moth in the family Noctuidae. This species is native to Australia. H. punctigera are capable of long distance migration from their inland Australian habitat towards coastal regions and are an occasional migrant to New Zealand.
The fall armyworm is a species in the order Lepidoptera and one of the species of the fall armyworm moths distinguished by their larval life stage. The term "armyworm" can refer to several species, often describing the large-scale invasive behavior of the species' larval stage. It is regarded as a pest and can damage and destroy a wide variety of crops, which causes large economic damage. Its scientific name derives from frugiperda, which is Latin for lost fruit, named because of the species' ability to destroy crops. Because of its propensity for destruction, the fall armyworm's habits and possibilities for crop protection have been studied in depth. It is also a notable case for studying sympatric speciation, as it appears to be diverging into two species currently. Another remarkable trait of the larva is that they consistently practice cannibalism, despite its fitness costs.
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Male accessory glands (MAG) in humans are the seminal vesicles, prostate gland, and the bulbourethral glands . In insects, male accessory glands produce products that mix with the sperm to protect and preserve them, including seminal fluid proteins. Some insecticides can induce an increase in the protein content of the male accessory glands of certain types of insects. This has the unintended effect of increasing the number of offspring they produce.
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