Attacks on corn by Spodoptera frugiperda require management

Spodoptera frugiperda, popularly known as the fall armyworm, is a lepidopteran insect that, in its larval stage, is considered the main cause of damage to various crops, especially corn. 

Originating in North America, the fall armyworm has easily adapted to the tropical climate, a factor that favors its proliferation. As it is a polyphagous insect, it has the capacity to cause damage to a wide range of crops. There are approximately 150 species susceptible to attack by S. frugiperda, with emphasis on corn (zea mays L.). Among the most harmful pests to the species, the insect stands out for feeding on the plant in all its stages of development, which can cause high losses, depending on the cultivar and also the environment. 

Several plant species can act as hosts for S. frugiperda, among them, soybeans (Glycinemax) - which is the most abundant legume in Brazilian agribusiness, and can play a fundamental role in the proliferation of insects when control is not carried out correctly. Corn is often grown in succession to soybeans, thus facilitating the spread of the fall armyworm in its more susceptible host. Considering that the damage caused to corn can reach approximately 39% of production, it is extremely important to control the pest in host plants.

Life cycle and characteristics 

Spodoptera frugiperda It is linked to the order Lepidoptera, which includes butterflies and moths. Its life cycle consists of four phases: egg, larva (which has different characteristics at the beginning and end of the phase), pupa and adult. 

The eggs of S. frugiperda They are laid on corn leaves, preferably at night. A female can lay between 150 and 350 eggs and has up to 13 clutches during her life cycle. In terms of color, immediately after laying they are light green, after 12 hours they turn orange, and darken even more as they approach hatching.

Incubation lasts a maximum of four days, however, it can be reduced to half that time in high temperature environments, as high temperatures are a factor capable of accelerating the maturation of eggs. 

The larvae immediately feed on the shells of newly hatched eggs and then attack the plant. This phase lasts between 14 and 23 days and consists of six or seven larval instars. The color of the larva also varies, from light green in the first instars to brown as the pupal stage approaches.

It is in the larval stage that the visual identification of S. frugiperda It becomes easier, since it has its own apparent characteristics. The corn earworm has an inverted “Y” on its forehead and black dots arranged in a square shape at the end of its abdomen. The larvae have three pairs of legs in the thorax region and five pairs of false legs on the abdomen.

After all larval stages have passed, the pupal stage occurs, which lasts between six and 55 days, under the influence of temperature. The pupa is reddish-brown in color and, at this stage, can be found among the corn husks, on the leaves, but mainly on the soil. 

Adults are moths that emerge at different times, depending on the length of the pupal phase. Females are grayish-brown in color and males are dark gray. These insects are highly mobile, measure approximately four centimeters, and this phase lasts an average of 12 days.

Attack symptoms

There are reports of the presence of fall armyworm in almost all cultivated areas in Brazil, however, its damage has been reduced with the use of treated and/or genetically modified seeds, with the implementation of integrated pest management (IPM), chemical and biological control.

The damage caused by S. frugiperda in corn, they occur both in the vegetative and reproductive phases of the plant. Initially, the caterpillars scrape the leaves, leaving them transparent. The leaves are mainly responsible for photosynthesis. Compromising the leaf area can lead to a decrease in productivity or even the death of the plant.

When it reaches a higher stage of development, the caterpillar begins to feed on the corn plant cartridge, which is located between the stem and the ear, and serves as a support base for the ear.

In the reproductive phase, damage can occur in the leaf area, such as where the ear is inserted into the plant, which can prevent the grains from filling completely or cause the ear to fall. On the ear, the attack initially occurs at the tip where the stigmas are located, which are the corn's “hairs” responsible for carrying the pollen grain to the plant's ovule. 

Control in focus

We hear a lot about the most common pest control methods in agriculture. Integrated pest management (IPM), with its most powerful tools, which puts into practice a set of actions - such as cultural control, mechanical control, chemical control, use of seeds of resistant varieties and/or cultivars - is often cited as a combatant against pest attacks. S. frugiperda in corn. In this context, with the increased search for efficient, highly durable products that cause less damage to the environment, biological products also emerged, which were added as tools within integrated management. 

In view of the importance of S. frugiperda As it causes damage to various crops, it is essential to adapt control measures to each plant species, but also to the needs of the producer, since the investment may be expensive and inappropriate for certain situations. 

*Per Luisa Laila Sousa da Silva, from the Santa Isabel II Farm