Comparative transcriptomic analysis of emamectin benzoate resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) from Puerto Rico

The fall armyworm (FAW), Spodoptera frugiperda J.E. Smith (Lepidoptera: Noctuidae), is a polyphagous invasive species that causes significant damage to corn crops worldwide. Emamectin benzoate (EB), a semi-synthetic insecticide derived from avermectin, targets the glutamate-gated chloride channel (GluCl) in nerve and muscle tissues, leading to paralysis in insects. EB is a highly effective active ingredient for controlling FAW; however, in Puerto Rico, its field efficacy at standard concentrations has been observed to decline. To assess whether resistance was the main factor behind the inadequate management of FAW, a field population was collected from Puerto Rico in 2023 (PR23). It was found that FAW developed very high levels of resistance to emamectin benzoate (34,000-fold). Moreover, to understand the genetics of this resistance, diet overlay bioassays were used to treat FAW larvae with emamectin benzoate and compare them with untreated controls in both resistant and susceptible populations (Benzon). Total RNA was extracted from the larvae of both populations for transcriptomic analysis. RNA-seq data indicated that PR23 was enriched in genes associated with insecticide metabolism and potentially linked to EB metabolism. Additionally, a single-nucleotide polymorphism (SNP) analysis was performed to identify mutations in the target gene. The findings of this study will offer a sequence-based approach to determine emamectin resistance in FAW populations in other regions as well as a proactive strategy for IRM/IPM globally.