Overexpression of ABC genes reduces the effectiveness of emamectin.

A fall armyworm (Spodoptera frugiperda) Moderate levels of resistance to the insecticide emamectin benzoate have been observed in field populations analyzed in China. Recent research has identified overexpression of genes from the ABC family as an important factor in this process.

The study evaluated six populations collected from different Chinese provinces. Toxicological assays indicated resistance ratios between 19,05 and 67,14 times that of the susceptible strain. The highest value occurred in the GDZJ population.

Laboratory selection further increased tolerance. After ten generations under insecticide pressure, the median lethal concentration increased from 0,021 mg/L to 5,37 mg/L. The resulting index reached 255,71 times higher than the susceptible strain. This level characterizes high resistance.

Cross-resistance

Further tests analyzed cross-resistance with other active ingredients. The resistant strain also showed strong resistance to abamectin, with a ratio of 22,45. The study recorded low resistance to indoxacarb. Lufenuron, chlorantraniliprole, deltamethrin, and cyantraniliprole maintained similar efficacy to the susceptible strain.

The investigation sought molecular mechanisms associated with the phenomenon. Transcriptome sequencing identified 3.770 differentially expressed genes. Among them, 2.108 showed increased expression in the resistant strain. Many of these sequences are related to transmembrane transport.

Among candidate genes, four transporters from the ABC family showed high expression in resistant populations: ABCD2, ABCC2, ABCG20a, and ABCB1. The analysis also found a positive correlation between expression level and LC50 value for emamectin.

RNA interference assays confirmed the functional role of these genes. Individual silencing reduced expression between 45% and 68%. After treatment with emamectin, larval mortality increased between 15,8% and 18%. Simultaneous silencing of all four genes increased mortality by 28,1%.

Tests with verapamil, an ABC transporter inhibitor, produced a similar effect. The compound increased the larvae's susceptibility to the insecticide by up to three times. The result indicates the participation of these transporters in the detoxification or expulsion of the compound from the cell.

Direct interaction

Molecular modeling also indicated a direct interaction between emamectin benzoate and the analyzed ABC proteins. Simulations showed hydrogen bonding and hydrophobic interactions at the protein binding sites. This pattern reinforces the role of these transporters in the transport of the insecticide or its metabolites.

The results indicate a significant role of metabolic mechanisms in increasing pest tolerance. The research also confirms the multifactorial nature of resistance in Spodoptera frugiperda.

More information at doi.org/10.1016/j.pestbp.2026.106980