FALL ARMYWORM (SPODOPTERA FRUGIPERDA): CHARACTERISTICS, LIFE CYCLE - BIOLOGY - 2025

The armyworm (Spodoptera frugiperda) is an insect of the order Lepidoptera (butterflies and moths), known as a major pest of maize. It is native to the American continent, with a tropical and subtropical distribution. This species has extended its natural range of distribution to other continents.

It has a complex life cycle, made up of four phases: egg, larva, pupa and adult. During the larval phase it is when it causes significant damage to the plantations. During this same phase it can feed on a wide variety of plants and even larvae of its own species.

Male of Spodoptera frugiperda. Taken and edited from: See page for author

For the management and control of Spodoptera frugiperda, multiple mechanisms have been used, ranging from the use, for example, of natural enemies, early detection of populations, insecticides to out-of-season cultivation of these insects.

characteristics

Because it is a species well known for causing damage to plantations or crops, the characteristics of this species of insect have been well studied in all phases of its life. These are the characteristics according to their stage of life:

Egg

It is hemispherical in shape (dome-like), grayish in color and measures about 0.4 millimeters in diameter and about 0.3 millimeters high. When the female lays the eggs, she puts a substance on top of it that gives the ovigerous mass a moldy and setose (similar to hairy) appearance.

Larva

The larvae go through six instars or stages. In each of these, the organism is morphologically different. In these six stages the width of the capsule of the head, as well as the length of the body, increase as it passes from one instar to another.

The mature larvae reach a size of 38 to 51 millimeters in length. On the forehead they have a characteristic inverted Y-shaped suture.

In the first days of the larval stage, they are greenish with a black head, when they move to the second stage, they retain their green color but the head changes to orange. At the end of the second instar and the beginning of the third, the larvae have a brown coloration on the body and lateral white bands or lines form.

In the last stages (4-6), the head becomes reddish-brown, with white or whitish spots, while the body is brownish with white lateral and sub-dorsal bands, has dark dorsal spots and presents spines.

Pupa

Usually the pupa spends its life in the ground, underground. It builds an oval cocoon about 20 to 30 millimeters long with materials found in the ground. The pupa can measure between 14 and 18 millimeters long and generally about 4.5 millimeters wide, and is reddish-brown in color.

Adults

The adult spodoptera frugiperda insect is nocturnal. It reaches a wingspan of between 32 to 40 millimeters (the distance between the two tips of the wings, when fully extended), while the length of the body is 20 to 30 millimeters. Adults are sexually dimorphic.

Male

With gray and brown forewings that have white triangular spots on the tips and in the central region of these. The hind wings are white and iridescent, with a narrow dark border (a characteristic shared by both sexes).

Female

They have less marked forewings, with a more uniform gray and brown coloration. On the other hand, the white spots on the tips of the wings and in the center of these (very conspicuous in males), are not present or are not very noticeable.

Taxonomy

The Spodoptera frugiperda moth is a species belonging to the phylum Arthopoda, subphylum Unirramia and the class Insecta (insects). Like the rest of the moths and butterflies, it is taxonomically located in the order Lepidoptera.

The genus Spodoptera is made up of at least 15 species. According to the morphological evidence of this group, the taxonomic identification is quite complicated, which is why they are considered cryptic species, that is, they are very similar morphologically but that meet the definition of species and are reproductively isolated. The separation of these species is generally done by molecular genetic analysis.

The species S. frugiperda is very similar morphologically to the species S. ornithogalli and S. albula. In addition, they can occupy the same geographic region, exploit similar resources and even the same ecological niche.

An investigation carried out in 2010 yielded information regarding the presence of subspecies within the species S. frugiperda.

Scientists believe that a divergence is occurring in two species and what supports this finding is, in part, genetic differentiation, preference for food (one prefers rice crops and the other corn) and reproductive behavior.

Lifecycle

The length of their life cycle, in days, varies considerably with the season of the year. During the winter this species can live up to 90 days, but in spring and autumn they have life cycles of 60 days. On the other hand, in hot areas or in summer, the species completes its cycle in approximately 30 days.

The species Spodoptera frugiperda, like other lepidopterans, is holometabola; In other words, they present complete metamorphosis, which, as already mentioned in the characteristics, present egg, larva, pupal and adult stages.

Egg

During the time of egg laying, the female usually lays around 100 to 200 eggs, but in her entire life she can lay up to 2000 eggs at most. The period or egg phase can take 2 or 3 days in summer, but depending on the temperature or the time of year, it can be more days.

Preferably, females lay their eggs under the leaves, but when populations are very high and spaces are scarce, they can deposit them almost anywhere in the environment.

Larva

The larva goes through 6 stages. The duration of each stage varies depending on the temperature or the season of the year. A study carried out in 1983 determined that at 25 ° C the times between each phase were 3.3; 1.7; 1.5; 1.5; 2.0 and 3.7 days respectively, between stages 1 to 6.

On the other hand, the complete larval cycle can last between 14 and 30 days and these time fluctuations also depend on the temperature and the season of the year.

Spodoptera frugiperda larva. Taken and edited from: See page for author (http://www.cbif.gc.ca).

Pupa

This phase of life takes place about 2 to 8 cm below the ground. The time this phase takes is from 7 to more than 30 days, depending on the environmental conditions of temperature or season of the year. In the lower periods or temperatures, the pupal stages can be longer.

Adult

Once the adults emerge from the ground and are almost ready to mate, the female goes through a period prior to laying her eggs (pre-oviposition) of about 3 or 4 days.

Mating occurs at night, when the females release a pheromone to attract males. Each female is able to mate only once per night.

Most of the eggs are laid in the first 4 or 5 days, but in some cases the oviposition can last up to 20 days. The entire adult cycle can last between 10 and 21 days.

Biologic control

For several years, the level of understanding about the damage that insecticides cause to the environment and to the organisms that live in it, producing poisoning in domestic animals, humans and death, not only of the species to which the program is directed, has been increasing. poison, but to others incidentally.

More and more reports indicate that pests are becoming resistant to these toxic substances, and this implies using greater amounts of insecticides or concentrating more doses, which in most cases double or amplify the damage.

The foregoing highlights the need to use biological controls in crops. These controls not only seek to reduce operating costs, but to eliminate the potential ecological and environmental damage caused by insecticides.

For the species Spodoptera frugiperda, several biological controls have been proposed such as:

Nematodes

Trials were carried out with the nematode Neoaplectana carpocapsae to reduce the populations of S. frugiperda in corn fields, finding that the infestation of the nematode on the moth larvae, under laboratory conditions, controlled them in a time of 48 to 72 hours..

During field tests the results were encouraging, but not conclusive.

Mushrooms

The Beauveria bassiana fungus has been shown, under laboratory conditions, to cause mortalities of up to 49.33% on S. frugiperda larvae in a period of 72 hours or 3 days. This organism seems to be even more effective against other insects, so it is not very used for the control of S. frugiperda larvae.

Bacteria

Several studies involving the bacterium Bacillus thuringiensis in biological controls of S. frugiperda larvae show a high mortality of the insect (70% or more). This means that, to date, the use of this microorganism is the most effective against this crop pest.

For greater efficiency, the researchers recommend obtaining the modified strain commercially and spreading it on the foliage of plants, before the first larvae of S. frugiperda appear.

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