Method makes it easier to differentiate "Chrysodeixis includens" from "Rachiplusia nu"

Researchers have developed a technique to quickly identify two common pests in South America, Chrysodeixis includens e Rachiplusia nu. The method uses the polymerase chain reaction (PCR) and allows the distinction between species through specific genetic profiles.

The study, led by scientists from Corteva Agriscience in Brazil and the United States, focused on the molecular identification of these pests, which are morphologically similar in the larval stage. This makes it difficult to recognize them in the field and, consequently, to adopt appropriate control strategies.

The research was based on variations in the mitochondrial cytochrome c oxidase I (COI) gene, creating specific primers that identify each species by distinct sizes of DNA amplicons.

Economic and environmental impact

Chrysodeixis includens e Rachiplusia nu cause significant damage to crops such as soybeans, sunflowers, cotton and tomatoes. Severe defoliation can result in losses of up to 80% of production.

even though Rachiplusia nu historically considered a secondary pest in Brazil, its increasing presence in transgenic soybean (Bt) plantations indicates changes in population behavior and resistance to insecticides.

The molecular method developed eliminates the need to rear caterpillars until they reach adulthood for identification, a technique previously used that required time and resources. In addition, PCR can be performed in standard laboratories, expanding access to the tool.

Field testing and validation

The researchers validated the technique with samples collected in non-transgenic soybean fields in the interior of São Paulo.

Of the 19 individuals analyzed, 16 belonged to the species Rachiplusia nu and three to Chrysodeixis includens, evidencing the co-occurrence of both species in the studied area.

According to the scientists, the tests proved that the method is accurate, fast and reliable, allowing for faster decisions in controlling infestations. Differentiation is critical, as each species has different susceptibilities to insecticides and Bt crops, requiring specific management strategies.

More information can be found at doi.org/10.3390/insects15120969