Spodoptera litura, commonly referred to as the tobacco cutworm or cotton leafworm, is a polyphagous pest in the family Noctuidae. As a nocturnal moth, it causes significant damage to a wide range of crops in Asia, mainly Cotton. The larvae of this species are notorious for their voracious feeding habits, often leaving the plants’ leaves completely decimated. The potential impact of S. litura on various crops and the agricultural economy has prompted efforts to control its populations.
Tobacco Cutworm management in Cotton
The life cycle of Tobacco Cutworm
- Eggs: spherical, slightly flattened, orange-brown or pink, laid in big batches on leaf surfaces
- Larva: 2.3mm to 32mm in length, light to dark green or brown color, feeds at night, six instar stages.
- Pupa: 15-20mm long, red-brown in color, two small spines at the tip of the abdomen
- Adult: 15-20mm long body, 30-38mm wingspan, gray-brown body, forewings with the dark gray, red, brown pattern, hindwings grayish-white with a gray outline, female longevity of 8.3 days, male longevity of 10.4 days.
- The Tobacco Cutworm completes 12 generations yearly, with life cycle length varying based on temperature.
Identification of the Tobacco Cutworm
- Eggs are found in masses and have a golden-brown appearance.
- The larva is Pale green with dark markings, typically seen in early-stage groups.
- Adult cutworms have forewings of Brown with wavy white markings and white hindwings with a brown patch along the margin.
Symptoms of damage by Tobacco Cutworm
- Cotton plants can be seriously damaged by cutworms, especially when the caterpillar population is high and the plants are young seedlings.
- These pests prefer to attack young crops at all growth stages and can cause severe harm.
- When young cutworms are present, they feed on the tender leaves of nearby weeds or cotton plants, leaving small irregular holes. Older cutworms burrow into the soil during the day to avoid the sunlight and come out at night to feed on the base of the cotton plants.
- This feeding can lead to young cotton plants being dragged underground or even cut off at the base, causing damage to the growing tissues, impeding growth, and in some cases, death.
- Additionally, the cutworms can burrow into the stem of older cotton plants, causing wilting and lodging, making it difficult for the plants to stand upright.
Impact/ favorable conditions of Tobacco Cutworm on Cotton crop
The favorable conditions for the increase in the population of S. litura are warm temperatures ranging between 10 to 37°C and various herbaceous plants as a food source. The ability of adult moths to fly up to 1.5 kilometers for 4 hours helps disperse the population into new habitats. It increases their chances of finding new food sources. The presence of warm temperatures and diverse food sources make tropical and temperate regions ideal for the growth of the S. litura population.