Spodoptera frugiperda

Spodoptera frugiperda It is widely known as the fall armyworm. Or, simply, fall armyworm.

Crops attacked

This species is highly polyphagous, attacking more than 100 host plants.

The main crops affected in Brazil include corn, soybeans, cotton, sorghum and rice.

In each crop, the caterpillar presents different behavior patterns and levels of damage.

Biology

Spodoptera frugiperda It has a relatively short life cycle, which favors its rapid multiplication and adaptation to different environments. This cycle is divided into four main stages: egg, larva, pupa and adult.

Eggs: Egg laying occurs in masses, usually on the upper side of leaves, with around 200 to 1.000 eggs per mass. The eggs are covered by scales on the moth's body, which partially protect them. The incubation period lasts on average three days.

Larvae: They go through six instars, lasting approximately 15 days in total. In their early stages, they feed gregariously, causing initial damage such as leaf scraping. As they grow, they become more mobile and spread throughout the plant, intensifying the damage. Cannibalism is common, especially in low-density infestations.

Pupae: After the larval stage, the caterpillars move to the soil, where they build pupal chambers. The depth of this chamber can vary, helping them survive during unfavorable periods, such as drought or cold. The pupal stage can last from 8 to 55 days, depending on environmental conditions, especially temperature and humidity.

Adults: The moths are grayish-brown in color and have a high dispersal capacity, being able to fly long distances. They live on average 15 days and begin to reproduce on the second day after emergence. Each female is capable of ovipositing more than 1.000 eggs throughout her life.

The high reproductive rate and short life cycle allow S. frugiperda rapidly colonize new areas and increase their populations in short periods.

Ecology and characteristics

The fall armyworm is a highly polyphagous species. It feeds on a wide range of host plants. It is estimated that more than 100 plant species can serve as food, with corn, soybeans, cotton, sorghum and rice being the main crops affected.

Climate adaptation: The pest is highly adaptable to different climates and regions. In Brazil, it finds favorable conditions to develop throughout the year, especially in tropical and subtropical areas. In regions with overlapping crops, such as corn and soybeans, the pest finds food continuously, favoring its permanence.

Food preferences and polyphagia: The polyphagous habit facilitates its adaptation to diverse agricultural systems. Crops such as corn and cotton offer preferred structures (such as cartridges in corn and bolls in cotton), while in soybeans, the caterpillar focuses on the pods and reproductive leaves.

Nocturnal behavior: S. frugiperda It is more active at night, which makes it less exposed to natural predators during the day. This habit also hinders the effectiveness of chemical controls applied during daytime hours.

Dispersal: Adult moths are capable of migrating long distances in search of new oviposition sites. This contributes to their rapid spread, which is an important factor in large agricultural areas.

Interaction with the agricultural environment: The proximity of susceptible crops, such as corn, cotton and soybeans, creates "green bridges", allowing the pest to continually find food and increase its populations. In addition, wild plants and cover crops, such as brachiaria and millet, also serve as refuge and food for the species.

Spodoptera frugiperda demonstrates high resilience due to its short biological cycle, high reproductive potential and ability to adapt to different agricultural systems. These factors, combined with the intensive use of insecticides and Bt technologies, have resulted in resistant populations in several regions of Brazil.

We also pack any Spodoptera frugiperda presents two genetically distinct lineages, known as the corn race and the rice race, widely recognized by the scientific community. The corn race is predominant in crops such as corn, cotton and sorghum. The rice race is more common in rice and pasture grasses, although there is overlap in hosts.

Studies such as those by Pashley (1986) and Saldamando-Benjumea et al. (2011) confirm genetic (COI and FR markers), behavioral (distinct pheromones) and physiological (intestinal microbiota) differences between breeds. These differences are important for integrated management strategies, considering variations in resistance to insecticides and toxins. Bt. Despite hybridization in the field, distinction between races is essential for effective control of this pest.

Damage

The damage caused by S. frugiperda vary depending on the crop attacked.

• Corn: destruction of the cartridge, reduction of the photosynthetic area and piercing of ears, compromising yield. The initial attack can lead to "dead heart", killing the young plant.

• Soybean: preference for reproductive structures, such as pods, causing a drop in productivity. The pest usually hides in protected areas of the plants, making chemical control difficult.

• Cotton: piercing of bolls and flower buds, as well as scraping of bracts and flowers.

Control

the management of S. frugiperda requires an integrated approach, combining different methods:

• Biological control: The use of parasitoids, predators and agents such as the baculovirus SfMNPV has demonstrated effectiveness in crop protection.

• Behavioral control: synthetic pheromones for monitoring and sexual confusion are promising, reducing pest reproduction.

• Cultural control: Strategies such as crop rotation and use of non-host plants reduce pest populations.

• Chemical control: Insecticides are still widely used, but pest resistance is a growing problem. Nighttime spraying is recommended to increase effectiveness.

• Bt Technologies: Genetically modified cultivars have offered partial protection. However, indiscriminate use has led to increased resistance.

Excerpts from scientific articles

Doi.org/10.1021/acs.jafc.4c03361 - Spodoptera frugiperda is a significant global pest, and chlorantraniliprole (CAP) is widely used in China for its control. Understanding CAP resistance in Spodoptera frugiperda is crucial for the effective management of this pest. Field populations exhibited varying degrees of CAP resistance (RR = 1,7–5,60 times). After 10 generations of selection, the CAP-resistant line developed resistance greater than 10 times, with a realized heritability (h²) of 0,10. Genetic analysis revealed autosomal, incomplete recessive, and monofactorial inheritance patterns. The CAP-resistant line showed limited cross-resistance to lufenuron and tetrachlorantraniliprole, negative cross-resistance to spinetoram, and no cross-resistance observed to other insecticides. Biochemical analysis suggested that P450-mediated detoxification is the main resistance mechanism, with 26 genes overexpressed in the CAP-resistant line. Furthermore, inhibition of CYP4L13, CYP6B39, CYP6B40, and CYP4G74 expression significantly increased the sensitivity of chloramphenicol-resistant larvae (CAP). These findings highlight the risk of CAP resistance in Spodoptera frugiperda and emphasize the crucial role of P450 enzymes in resistance.

Doi.org/10.1002/ps.5812 - The inheritance pattern of resistance to spinetoram in Spodoptera frugiperda was characterized as autosomal, incompletely recessive, and polygenic. Cross-resistance between spinosyns was confirmed in Spodoptera frugiperda. The importance of this information for implementing insect resistance management strategies is discussed in this article.

Doi.org/10.1002/ps.5376 - The frequency of the chlorantraniliprole resistance allele was moderately high in a field-collected population of Spodoptera frugiperda. The inheritance of chlorantraniliprole resistance was characterized as autosomal, incompletely recessive, and monogenic. Spodoptera frugiperda showed cross-resistance to other diamide insecticides. These results provide essential information for the implementation of Integrated Pest Management (IPM) programs aimed at preserving the useful life of diamide insecticides in the control of Spodoptera frugiperda in Brazil.

Doi.org/10.3390/insects17050460 - The fall armyworm (Spodoptera frugiperda) has been characterized by the widespread development of tolerance to multiple insecticides, a process facilitated by extensive and prolonged exposure to these compounds. This study used RNA interference (RNAi) to explore the possible association of cytochrome P450 genes with spinetoram resistance in Spodoptera frugiperda, with the parallel objective of investigating P450-targeted nanocapsule-based formulations as synergistic agents for better pest management. Bioassay results in Spodoptera frugiperda populations from Guangdong revealed the highest tolerance in the Meizhou population (LC50 = 0,673 µg/mL). Exposure to spinetoram induced a 6,5 U/mL increase in larval P450 activity and triggered a marked upregulation of CYP6AN4 (4,98 times compared to the control), which exhibited concentration-dependent induction (2,52 times under the tested conditions). The LDH-dsCYP6AN4 + spinetoram formulation achieved 62,87% mortality, representing an 11,31% increase compared to the LDH + spinetoram group, and maintained robust synergy across various field populations. These phenotypic and molecular observations indicate that CYP6AN4 upregulation is closely correlated with the response to spinetoram and may potentially contribute to altered insecticide susceptibility in field populations.