EN 
PT_BR Joint research conducted between the University of Brasília (UnB) and Embrapa Genetic Resources and Biotechnology (DF) has unveiled the chemical "dialogue" between corn and the fall armyworm (Spodoptera frugiperda), one of the most damaging pests to the crop. The 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 spectabilis), a companion plant to corn. 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.
Photo: Cláudio Bezerra
The study, led by master's student Bruna Sartório de Castro (UnB) under the supervision of researcher Maria Carolina Blassioli-Moraes, from Embrapa, 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 (photo on the right), 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.
Photo: Ana Lúcia Ferreira
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.
How science deciphers volatiles
To validate the identified volatile compounds, the research team – composed 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 the separation and identification of the different "perfumes" emitted by plants. This technique was fundamental for isolating and cataloging the 12 compounds that corn releases and which, according to the study, are the attractants for the fall armyworm.
Photo: Luiz Alberto Marsaro Júnior
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.
