Study reveals how corn attracts fall armyworm.

A joint research project developed between the University of Brasília (UnB) and Embrapa Genetic Resources and Biotechnology (DF) has unveiled the chemical "dialogue" between corn (zea mays) and the fall armyworm (Spodoptera frugiperdaThe study, published in the Journal of Pest Science, identified the volatile compounds, or chemical "perfumes," that corn releases to attract the insect.

The research also confirmed the defense mechanism of crotalaria (Crotalaria spectabilisCrotalaria, a companion plant to corn, has been found to be a valuable addition to the crop. This discovery not only explains why crotalaria is an effective ally in pest management, but also scientifically validates its use as a physical barrier and a low-cost alternative, especially for small and medium-sized farmers.

The study, led by master's student Bruna Sartório de Castro (UnB) under the supervision of Embrapa researcher Maria Carolina Blassioli-Moraes (pictured below), proved that infested corn releases 12 volatile compounds that act as attractants for female fall armyworms. In contrast, crotalaria produces a different composition of volatiles, which makes it unattractive to the pest.

According to Blassioli, the current research is an offshoot of two other studies, conducted by Embrapa Maize and Sorghum (MG) and Embrapa Genetic Resources and Biotechnology, which observed in the laboratory and in the field, respectively, a positive effect of using crotalaria as a companion plant for maize in the management of the fall armyworm. “The objective of this new work was to understand what the mechanism for this effect would be. We wanted to evaluate whether crotalaria could emit some volatile compound to repel the insect or if it was just a physical barrier,” he explains.

Crotalaria in the field: a natural and accessible barrier.

The research validated the strategy of planting crotalaria on the edges of cornfields, creating a physical barrier that protects the corn plants and naturally reduces infestation. This low-cost solution is an alternative to traditional methods, such as the use of genetically modified corn (Bt corn), which can be expensive and raise concerns about the development of long-term pest resistance. Furthermore, it is an important control method for organic farming and other agroecological systems.

Although some small Brazilian producers already use crotalaria as a companion plant, the research provides the scientific basis for understanding the mechanism behind the success of this strategy. According to the Embrapa researcher, this knowledge is crucial so that, in the future, the genetic improvement of plants does not affect this beneficial interaction with other organisms.

The team's next step, as Blassioli explains, is to take the knowledge from the laboratory to the field, working together with small producers. The idea is to propose and monitor experiments that validate the use of crotalaria as a companion plant on a larger scale, evaluating its long-term effect on pest control. "This collaboration will not only test the effectiveness of the technique under different growing conditions, but will also provide practical data to improve integrated management strategies," he adds.

New possibilities for sustainable agriculture

Identifying the attractive compounds in corn also paves the way for new integrated pest management (IPM) technologies. The researcher highlights the potential for developing synthetic baits based on these volatiles to attract fall armyworm moths to traps, reducing the need for insecticides.

The compounds that corn uses to attract the moth can be used in synthetic formulations. "Although we have identified 12 compounds, there is likely to be redundancy. If we can reduce this mixture to a smaller number of substances, the production of a bio-input becomes more economically viable," points out Blassioli. She suggests that, in the future, these compounds could also be used to modify other plants to produce different combinations of volatiles, confusing the pest.

How science deciphers volatiles

To validate the identified volatile compounds, the research team – comprised of Carolina Blassioli, Miguel Borges, and Raul Laumann – used a two-step approach. The first phase employed gas chromatography coupled with mass spectrometry (GC-MS), an analytical method that allows for the separation and identification of the different "perfumes" emitted by plants. This technique was fundamental in isolating and cataloging the 12 compounds that corn releases and which, according to the study, are the attractants for the fall armyworm.

After identifying these chemical elements, the second step consisted of testing the moths' response in the laboratory. For this, a wind tunnel was used, equipment that simulates ambient air currents in a controlled manner. In this tunnel, female fall armyworms were exposed to different odors: that of infested corn, that of crotalaria, and a synthetic mixture of the compounds identified via GC-MS.

The results were clear: the moths flew towards the smell of the corn and the synthetic mixture, confirming that the identified substances are, in fact, responsible for attracting them. Conversely, they showed no attraction to the aroma of the crotalaria. This double validation—chemical and behavioral—provided the scientific basis to affirm that crotalaria does not attract the pest and, therefore, acts as an effective barrier.

The destructive legacy of the fall armyworm.

The fall armyworm (Spodoptera frugiperdaThe corn weevil (Citrus aureus) is one of the most destructive pests for Brazilian agriculture. According to information from Embrapa, this insect is highly polyphagous, meaning it attacks not only corn but also several other economically important crops in the country, such as soybeans, cotton, and rice.

According to data from the Ministry of Agriculture and Livestock (Mapa), the pest insect is especially voracious in corn plantations, attacking the plant in all its stages of development. The caterpillars feed on the leaves and the whorl, the central part of the plant, causing direct damage that can lead to a drastic reduction in productivity and, in cases of severe infestations, to the total loss of the crop.

The insect's great adaptability, coupled with its rapid life cycle and ability to generate multiple generations in the same crop, makes controlling it difficult. Spodoptera frugiperda a constant challenge for rural producers.