Spodoptera frugiperda loses sensitivity to chlorantraniliprole in Argentina

A new technical alert from the Argentine No-Till Farmers Association (Aapresid) has brought renewed attention to the risks of resistance in Latin American cropping systems. According to its pest monitoring network (REM), populations of Spodoptera frugiperda in northern Argentina are already showing reduced sensitivity to the widely used insecticide chlorantraniliprole—a development that could reshape control strategies in maize and soybean.

The findings are based upon research conducted by teams from the National Institute of Agricultural Technology (INTA) in Marcos Juárez and Reconquista, and are being treated as an early warning signal rather than a confirmed case of field-level resistance. Even so, the data points to a measurable shift in susceptibility that demands close monitoring.

A shifting efficacy landscape

Laboratory bioassays revealed that a population collected in Reconquista in September 2025 required significantly higher doses of chlorantraniliprole to maintain control. The median lethal concentration (LC₅₀) was 21 times higher than that observed in a reference population from Marcos Juárez and nine times higher than samples from La Cocha.

This reduced sensitivity emerges in a context in which chemical control has regained prominence. Over the past two seasons, reports of unexpected damage in maize hybrids expressing the Vip3Aa20 trait have led to increased insecticide applications, intensifying selection pressures on pest populations.

For more than a decade, Vip3Aa20 delivered high levels of control against fall armyworm. However, recent inconsistencies in field performance have pushed growers to rely more heavily on diamide insecticides, such as chlorantraniliprole, raising concerns about long-term sustainability.

Early warning, not yet failure

Specialists emphasize that the current findings should not be interpreted as a loss of control, but rather as a critical early-stage signal. If selection pressure continues, the tolerance observed today could evolve into operational resistance in the near future.

The monitoring network of the Argentine No-Till Farmers Association highlights that this is precisely the stage at which management strategies can still be adjusted effectively, before widespread field failures occur.

Rethinking pest management

The report reinforces the importance of integrated pest management (IPM) principles. Monitoring intervals should be shortened, particularly during warm periods that accelerate pest development. Also, interventions must be based on population thresholds, rather than routine applications.

Timing remains decisive. Applications targeting early larval stages (L1–L2) are significantly more effective, while late sprays—when larvae are already protected within the plant whorl—tend to fail and increase selection pressures.

Application quality is another key factor. Parameters such as droplet size, uniformity of coverage, spray stability and drift control can determine outcomes, ranging from highly effective control to poor performance.

Rotation and diversification as strategic pillars

A central recommendation is the strict rotation of modes of action. Avoiding the repeated use of insecticides with the same target site within short generational windows—typically around 30 days—is essential to delay the evolution of resistance.

The Argentine case reflects a broader structural trend: as biological and genetic tools face increasing pressure, the durability of chemical solutions will depend less on new active ingredients and more on how existing technologies are managed.

For the Argentine No-Till Farmers Association and the National Institute of Agricultural Technology, the message is clear—this is a window for proactive action. Strategic adjustments made now will be decisive in preserving the efficacy of key insecticides across South America’s major cropping systems.