Spodoptera litura

Spodoptera litura, otherwise known as the tobacco cutworm or cotton leafworm, is a nocturnal moth in the Noctuidae family. S. litura is a serious polyphagous pest in Asia, Oceania, and the Indian subcontinent that was first described by Johan Christian Fabricius in 1775. Its common names reference two of the most frequent host plants of the moth. In total, 87 species of host plants that are parasitized by S. litura are of economic importance. The species parasitize the plants through the larvae's 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. Their potential impact on the many different cultivated crops, and subsequently the local agricultural economy, has led to serious efforts to control the pests. 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. 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 mm while female forewing length is slightly larger and measures 15–18 mm. The orbicular spot on the forewing is also more pronounced in the males. 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. 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. Since both species are polyphagous, taking note of the host plant is not helpful in correct identification. 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. S. litura is the most common in South Asia. However, its natural range extends from the Oriental and Australasian areas to parts of the Palearctic region as well. The countries with the most widespread population of S. litura include but are not limited to China, Indonesia, India, Japan, and Malaysia. 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. S. litura is a general herbivore and takes residence on various plants. The lower and upper limits of habitable temperatures are 10 °C and 37 °C, respectively. Therefore, it is well suited for tropical and temperate climate regions. As caterpillars, S. litura can only move short distances. However, adult moths can fly up to a distance of 1.5 km 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. 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.