Spodoptera frugiperda: a significant threat to Brazilian agriculture

By Alejandro Sandria Díaz, Geísy Nascimento Leal, Nadiane França da Silva, Maria Gabriela Silva Venâncio, Karolina Gomes de Figueiredo, Júlia Assunção de Castro Oliveira and Nathan Jhon Lopes, from the Federal University of Lavras

31.07.2024 | 14:48 (UTC -3)

Corn is a highly plastic crop and has enormous economic and cultural importance, present both in family farming and among large producers. Harvest estimates for the next harvests exceed 100 million tons. Due to its low cost, there is a wide supply in all regions of Brazil and a high nutritional quality, providing energy for monogastrics and being a source of fiber and carbohydrates for ruminants. 

Despite the great importance of this crop on the national and international scene, it is affected by abiotic and biotic factors that contribute to losses in productivity. A Spodoptera frugiperda, popularly known as the corn armyworm, is a pest that has caused great concern in the Brazilian and global agricultural sector. This species of moth, originally from the Americas, stands out for its high adaptability and voracity, being able to attack a wide range of crops, including corn, soybeans, cotton, sorghum and wheat.

The rapid dissemination and resistance to several insecticides make the management of S.Podoptera frugiperda an ongoing challenge for farmers. Integrated control strategies, including constant monitoring, the use of natural enemies, integrated pest management (IPM) techniques and crop rotation, are essential to mitigate the impacts of this pest.

Given the economic importance of affected crops and the need to ensure food security, understanding and effective control of Spodoptera frugiperda are extremely relevant for Brazilian agriculture. Therefore, continuous research and implementation of sustainable management practices are essential to protect crops and ensure agricultural productivity in the country. 

Biology and ecology

A Spodoptera frugiperda It is a polyphagous pest with a nocturnal habit, its development is of the holometabolic type, comprising the stages of egg, larva, pupa and adults. Its total life cycle time varies between 32 and 46 days, which can be directly affected by biotic and abiotic factors. 

Its occurrence in Brazil, due to its diversification of food and successive crops, allows the survival of high populations and periodicity of moths between host crops, in addition to the favorable climate for the insect, making its occurrence general in all regions of the country . 

The eggs, light green in color, are laid en masse, both on the upper and lower sides of the leaf. The larvae go through six stages of development, between 14 and 30 days, they present, on the dorsal extension of their body, three longitudinal lines of yellowish white color, their head has a dark color with sutures that cross each other forming an inverted “y” and four black dots on the dorsal part of the last abdominal segment, a characteristic mark of the species and the means by which its identification occurs (Figure 1). 

Figure 1: main identification points of Spodoptera frugiperda; photo: Maria Gabriela Venâncio (2024)
Figure 1: main identification points of Spodoptera frugiperda; photo: Maria Gabriela Venâncio (2024) 

At the end of the larval period, the caterpillars, approximately 50 mm long, enter the soil, where they transform into reddish pupae. The pupae, approximately 15 mm long, are hidden in the soil or on the plant and last between eight and 13 days. After emergence, the moth appears with an average wingspan of 35 mm, and a life expectancy of approximately ten to 15 days.

Copulation of this insect occurs at night. The adult female can oviposit more than two thousand eggs. In this species, sexual dimorphism also occurs, that is, males and females are different. Males have forewings with two light spots, distinguishing them from females. 

The damage caused by this pest is numerous and can vary according to the species of plant attacked, the phenological stage, the season and the intensity of infestation. In corn cultivation, for example, damage occurs from the attack of young leaves that are scraped off in the initial stages of S. frugiperda; From the 3rd stage onwards, the caterpillar penetrates the cartridge, also destroying several points of the leaf as it feeds. This is a way of recognizing the caterpillar in the field, by checking the damage caused, such as the tearing of leaves (Figure 2), the perforation of stalks and ears (Figure 3).

Figure 2: presence of Spodoptera frugiperda on corn leaves in the field; photo: Maria Gabriela Venâncio (2022)
Figure 2: presence of Spodoptera frugiperda on corn leaves in the field; photo: Maria Gabriela Venâncio (2022) 
Figure 3: presence of Spodoptera frugiperda on corn cobs in the field; photo: Maria Gabriela Venâncio (2022)
Figure 3: presence of Spodoptera frugiperda on corn cobs in the field; photo: Maria Gabriela Venâncio (2022) 

When feeding on leaves, S. frugiperda reduces leaf area, which directly affects production. It is estimated that its damage can result in a 20 to 60% reduction in productivity. The high degree of polyphagy further promotes the population dynamics of the caterpillar, causing migrations to favor population outbreaks in different cultures.

Monitoring and sampling

Spodoptera frugiperda It is an extremely important pest in crops such as corn and other agricultural crops. The life cycle of this insect pest is relatively short, around 30 days, in which the larval phase is responsible for the greatest damage to plants. During this period, caterpillars intensively consume leaves and other parts of plants, significantly reducing crop yields. In addition to direct damage, this pest also facilitates the entry of pathogens into plants, further increasing economic losses.

Analysis of the conditions of the agricultural environment or agroecosystem consists of obtaining information about planting, such as the crop's growth phase, the plant's nutritional needs, the climate, the main pests that can cause damage and the presence of natural enemies. Monitoring and sampling are very important to determine the level of economic damage caused by the pest to the crop, allowing the identification of the predominant direction of pest entry, the natural enemies present and, most importantly, predicting the best time to carry out control. 

In corn cultivation, sampling is recommended by dividing the area into plots, and standardizing sampling in a zigzag or perimeter model, with five sampled locations. It is recommended to sample 20 plants per point, in five points per plot. The assessment of damage caused by the fall armyworm to corn is done through direct observation and, when 20% of the plants reach a damage score of three on the Davis scale (elongated lesions from circular scraping on the leaves), it is recommended to take measures decisions to control the pest. 

Among the most common monitoring and sampling techniques for the fall armyworm, the following stand out: pheromone traps (with synthetic pheromones that attract adult males), with one trap per hectare and a control level of three moths per trap; visual sampling (detection of the presence of eggs, young caterpillars or leaf damage); sampling by beating cloth (allows quick and efficient counting of the presence of the pest); damage monitoring (evaluates damage levels such as defoliation and leaf injuries); meteorological monitoring (monitors temperature and humidity); and data analysis and decision making (to develop appropriate control strategies). These sampling and monitoring techniques are fundamental for effective integrated pest management, aiming to minimize the impact of S. frugiperda on agricultural crops. Therefore, monitoring and sampling S. frugiperda are essential practices to promote sustainable and efficient agriculture, minimizing damage caused by pests, while optimizing the use of resources such as pesticides and other control methods.

control methods

For the integrated management of fall armyworm in corn crops, some control tactics are used to keep the insect population below the level of economic damage. Such as, for example, cultural control, biological control, genetic control, chemical control and use of botanical extracts (Table 1).

Cultural control must be carried out at the beginning of cultivation. The producer must observe whether the pest is present in the area and control it. Another commonly used practice is the destruction of cultural remains from the previous harvest.

Biological control consists of the use of natural enemies to control pests and can be classified as conservative, inoculative or inundative. The adoption of actions with less impact on natural enemies characterizes conservative control. Thus, we can mention the planting of species that supply pollen or nectar and the use of selective pesticides against predatory insects or parasitoids of the target pests. For inoculating and inundative control, there are biofactories that sell products based on macro and microorganism agents. To preserve the efficiency of bioinputs, caution is required in storage, and transportation and dosages are previously recommended. Currently, the use of drones is a technological tool to optimize the dispersion of biological products. 

Bt corn is the result of transgenics between corn and bacteria Bacillus thuringiensis and promotes the control of caterpillars, mainly from the Lepidoptera order. Feeding transgenic corn leaves causes the death of pests, due to the activation of toxins in the stomach. This technology must be accompanied by the implementation of refuge areas, which is the planting of non-Bt species alongside transgenic corn to preserve the technology (Figure 4).

Figure 4: association between BT corn and conventional corn; photo: Maria Gabriela Venâncio (2024)
Figure 4: association between BT corn and conventional corn; photo: Maria Gabriela Venâncio (2024) 

Chemical pest control can be applied from planting to the final stage of cultivation. Initially, the preventive method is used, treating seeds with chemical substances in areas with a history of infestation. Sprays are carried out when the pest reaches the control level, using insecticides that affect the physiology of the insects to eliminate them. Chemical groups such as pyrethroids, carbamates, diamides, avermectins, oxadiazines, spinosins and growth regulators can be used. It is crucial to rotate modes of action (Figure 5), so that there is no selection of a population of resistant insects, as well as using doses recommended on the product label or leaflet. Another factor of great importance is to recommend products that do not affect natural enemies, as they also help to reduce the pest population. Substances extracted from plants can also be used to control pests. An example of this are essential oils, which are secondary metabolites present in plants that can negatively affect pests. The essential oil of a plant popularly known as Neem is registered for the control of fall armyworm.

Figure 5: rotation by insecticide mode of action; photo: Maria Gabriela Venâncio (2024)
Figure 5: rotation by insecticide mode of action; photo: Maria Gabriela Venâncio (2024) 
Table 1: Biological control methods with macro and microorganisms and chemical control that can be used for Spodoptera frugiperda
Table 1: Biological control methods with macro and microorganisms and chemical control that can be used for Spodoptera frugiperda

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