Characterisation of Sex Pheromone and Genetic Strain in <i>Rachiplusia nu</i> (Lepidoptera: Noctuidae) Populations Across Brazil

ABSTRACT Rachiplusia nu , known as the sunflower looper (SFL) and belonging to the Plusiinae subfamily, is a major defoliator of soybeans, sunflowers and other horticultural crops across southern South America. This species has recently expanded to central and northern regions of Brazil, becoming a key soybean pest. Here, we aim to identify the sex pheromone of R. nu and characterise its genetic strains, followed by preliminary field bioassays to evaluate pheromone effectiveness in insect attraction. Genetic analysis revealed a single mitochondrial DNA (mtDNA) strain of R. nu across Brazil, Argentina, Paraguay and Uruguay, characterised by low nucleotide and haplotype diversity. A dominant mtDNA haplotype (frequency = 0.7) was found across all regions sampled. Gas chromatography coupled with electroantennographic detection (GC‐EAD) and mass spectrometry (GC–MS) analyses of female R. nu aeration extracts identified a female‐specific compound, which was determined to be ( Z )‐7‐dodecenyl acetate. This identification was confirmed through microderivatisation of natural extract, the mass spectrum comparisons and co‐injections with authentic standards. Laboratory and field bioassays confirmed the biological role of this compound as a sex pheromone. The observed low genetic diversity in R. nu likely explains the minimal variation (or absence) of sex pheromone components across the three tested populations. The identified pheromone, previously recognised in other species, holds potential for use in pest monitoring and management strategies. R. nu exhibits a monocomponent sex pheromone, classified as a type 1 lepidopteran pheromone.