Tobacco cutworm

Appearance

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.

Naming

''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.

Behavior

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.

Habitat

''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.

Reproduction

Larvae body length ranges from 2.3 to 32 mm. 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 800 mg.

Food

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.

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 insects and 12 species of spiders 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. 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.