Overview
- What is Spodoptera litura?
- What is the impact of Spodoptera litura?
- How do I know if I have a Spodoptera litura problem?
- How do I get rid of Spodoptera litura?
- Summary
Spodoptera litura is a polyphagous pest, which means it has a wide host range. It is also known as the tobacco cutworm, tobacco caterpillar, taro caterpillar, oriental leafworm moth, and cotton leafworm. This pest causes damage to many crops during its larval (caterpillar) stage. It has a wide geographical distribution across Africa, Europe, and Asia, including Bangladesh, where it damages many economically important crops, including cabbage. This article will cover what Spodoptera litura is, how to identify it, the damage it causes, and methods for getting rid of infestations, including biological control methods.
What is Spodoptera litura?
Spodoptera litura is a species of moth that causes significant damage to economically important crops. Females lay eggs on host crops, and after a few days, young larvae begin feeding on plant tissue. Several species of moths are similar in appearance to Spodoptera litura, including Spodoptera littoralis, beet armyworm (Spodoptera exigua), and fall armyworm (Spodoptera frugiperda). It can be very challenging to tell these species apart without expert knowledge and experience.
Spodoptera litura adults are 14-18 mm long and have white-brownish bodies with a pale red tinge. Orange and light brown hairs run along the back of the body. The forewings (closer to the head) have a dark brown colour with light brown stripes, and the hindwings (further from the head) are pale whitish with a violet sheen with a dark brown border.
Females are slightly bigger than males, with a wingspan of 15-18 mm compared to 14-17 mm, and lay white round eggs that are 0.4 to 0.7 mm in diameter. Orange or pink scales from the female’s body usually cover the eggs.
Below are examples of moths that look a lot like Spodoptera litura but are actually distinct species.
Credit: Robert J. Bauernfeind, Kansas State University via Bugwood.org
Newly hatched Spodoptera litura larvae are tiny and black-green in colour but can grow to a maximum size of 40-50 mm. Fully mature larvae have black spots on their first and eighth abdominal segments, though their overall colour varies between black, dark grey, and dark brown. The larvae also have yellow-green stripes along their back and white stripes along the sides. Pupae are red-brown in colour, about 20 mm long, and are found in the soil.
Life cycle
Spodoptera litura progresses through egg, larval, pupal, and adult stages. Females lay hundreds of eggs at once on the underside of leaves during June, July, and August, and eggs hatch 3-12 days later, depending on the season. Eggs laid in warmer seasons hatch days faster. Newly hatched instars progress through six developmental stages before forming pupae. The pupal stage lasts 7-10 days and takes place in soil, and adult females begin egg production 2-5 days after emerging from the pupa. The duration of the life cycle depends on factors like temperature and humidity. This pest can have up to 12 generations per year depending on local conditions
What is the impact of Spodoptera litura?
Spodoptera litura larvae cause harm by feeding directly on various plant parts. While they primarily target the leaves of their host plants, they can also damage tubers and root systems, depending on the plant species and the larvae’s stage of development. Extensive leaf damage can lead to stunted plant growth. More mature larvae also feed on the fruit, leading to premature ripening and wateriness of plant tissue. This makes the fruit inedible. This pest attacks a wide range of plants (up to 120 species), including tomatoes, corn, potatoes, sugar beet, cotton, onions and cabbage.
In Bangladesh, this pest accounts for up to 58% of cabbage plant damage. These effects have a significant economic impact and necessitate costly control methods to reduce Spodoptera litura numbers. Large infestations can lead to rapid destruction of entire plants.
How do I know if I have a Spodoptera litura problem?
Early signs of Spodoptera litura include damage to leaves and discolouration, damage to plant stalks, and damage to pods and fruits. Larvae tend to feed on softer tissue on the underside of plants, leading to a “windowing” effect. They may also avoid eating leaf veins, leading to a “skeletonising” pattern. Patches of eggs may also be visible on the underside of leaves covered in the characteristic orange or pink hair scales. Larvae will also be visible on plants, especially in the later instar stages. Signs of a large infestation include complete defoliation of plants.
How do I get rid of Spodoptera litura?
Fortunately, many methods are available for monitoring and controlling Spodoptera litura numbers, including biological control methods that are safer for the environment unlike chemical pesticides.
Monitoring
Monitoring is a crucial step in controlling Spodoptera litura populations because it helps to confirm that they are the species responsible for the problem. This allows for more targeted control methods and helps assess the severity of the infestation. Traps are the best way to monitor the numbers of these pests. Semiochemicals are chemicals that organisms use to communicate with each other for mating and other purposes. Semiochemicals like spodolure can be used in traps to lure adult moths. You can also monitor Spodoptera litura infestations by scouting for egg patches on the underside of leaves or looking for signs of leaf damage like “windowing” and “skeletonising”.
Mechanical control
While traps can be considered mechanical control, they are not used to directly reduce Spodoptera litura numbers. It is possible to collect and destroy larvae and egg masses mechanically using methods like handpicking. Alternatively, protective screens or nets can be used to prevent egg-laying by adults.
Biological control
Biological control methods use pest solutions derived from nature, including microorganisms, larger invertebrate species, and natural predators (macrobials) that prey on Spodoptera litura. These methods provide a more sustainable alternative to chemical pesticides and cause minimal or no damage to the ecosystem.
Natural Substances
There are several natural substance solutions for dealing with Spodoptera litura populations. These products are typically derived from plants, and many, such as neem oil, are effective against a broad range of pests and can be sprayed directly onto plants. Wrath Insecticide is a combination of several natural substances, including cottonseed and peppermint oil that are effective against Spodoptera litura.
Microbials
Several microbial solutions are available to control Spodoptera litura numbers. Species like the Bacillus thuringiensis bacteria and Beauveria bassiana fungi are lethal to this pest. Bacillus thuringiensis kills the larval stage of this pest by releasing toxins when it is consumed. When B. bassiana spores come into contact with Spodoptera litura they grow through the cuticle (skin) of the pest and eventually kill by causing a systemic infection; this fungus does not need to be ingested. Viruses, such as nucleopolyhedrovirus (NPV), can also help control the numbers of this pest by causing lethal infection in the larval stage.
Macrobials
Parasitic wasps, such as the species Trichogramma chilonis, are a useful way to combat this pest. These wasps lay their eggs inside the eggs of Spodoptera litura. When the wasp eggs hatch, they consume Spodoptera litura before they reach adulthood.
Chemical pesticides
As a world leader in nature-based pest management knowledge implementation, CABI encourages Integrated Pest Management (IPM)as the preferred, ecologically-based approach to producing healthy crops, which allows for chemical pesticide use only as needed, and when adhering to measures that limit the exposure of people and the environment to them (see FAO, International Code of Conduct on Pesticide Management).
Before considering the use of chemical pesticides, farmers should explore all available non-chemical control solutions. These might include practices like handpicking caterpillars and scraping egg masses and consulting the CABI BioProtection Portal for identifying and applying suitable biological control products.
In case chemical pesticides are considered for use, farmers should look to select lower-risk chemical pesticides which, when used as part of an IPM strategy, help manage pest problems while minimizing harmful effects on human health and the environment. Agricultural advisory service providers can provide information on lower-risk chemical pesticides that are locally available and are compatible within an IPM strategy. These experts can also advise on the required personal protective equipment.
Summary
Spodoptera litura is a highly destructive pest that affects a wide variety of economically important crops. Its larvae cause extensive damage, leading to stunted growth and unmarketable products. Identifying infestations early through monitoring methods like traps and scouting for eggs is crucial. Chemical pesticides are common control methods, but they pose risks to both the environment and human health and have led to resistance. Biological control methods, including microbial solutions, natural substances, and parasitic wasps, offer more sustainable and eco-friendly alternatives for managing Spodoptera litura populations and reducing the need for harmful chemicals.
Our resources page provides information about control methods for other pests, such as the bean fly. You can also browse the CABI BioProtection Portal to find environmentally friendly solutions to your pest issue.
