COI HAPLOTYPE ANALYSIS REVEALS PREDOMINANCE OF CORN-ASSOCIATED LINEAGES OF Spodoptera frugiperda IN SARAWAK, EAST MALAYSIA

Abstract

The fall armyworm (Spodoptera frugiperda (J.E. Smith, 1797)) is a highly invasive agricultural pest of global economic importance, comprising two host-associated strains, the corn (C-strain) and rice (R-strain) that differ in ecology and management responses. Since its first detection in Malaysia in 2019, this species has become a persistent threat to corn production; however, information on its strain composition in Sarawak remains limited. This study characterised the strain structure and distribution of fall armyworm populations from major corn-growing regions in Sarawak using mitochondrial cytochrome oxidase I (COI) DNA barcoding. A total of 39 specimens collected from five localities were analysed through PCR amplification, sequencing, and phylogenetic comparison with global reference haplotypes. The results revealed a strong predominance of C-strain-associated COI haplotypes (89.7%) across all sampling sites, consistent with host-associated patterns reported throughout Southeast Asia. In contrast, R-strain haplotypes were detected at low frequency and were restricted to Bintulu and Samarahan. Haplotype clustering analyses showed close genetic affinity between Sarawak populations and previously reported invasive lineages, consistent with previously reported COI haplotypes from invaded regions. The coexistence of strain-associated haplotypes in localized populations may indicate ecological overlap or potential interstrain mixing; however, interpretation is constrained by the maternal inheritance of mitochondrial markers. Consequently, COI-based strain assignments should be treated cautiously and do not necessarily reflect biologically distinct host-associated populations. Despite these limitations, this study provides baseline molecular evidence of FAW strain composition in Sarawak and highlights the need for continued multi-marker surveillance to support strain-informed integrated pest management strategies for corn and other susceptible crops.