Genetic Profiling of Spodoptera litura (Noctuidae: Lepidoptera) in Indian Sub-Tropical Sugar Beet

Abstract

The armyworm, Spodoptera litura Fabricius, 1775 (Noctuidae: Lepidoptera) is a serious and emerging insect pest of sugar beet in India, resulting in significant yield losses. A phylogenetic tree was constructed using the CLUSTAL W and neighbour joining technique, and a neighbour joining haplotype network was formed using PopArt to assess the relationships between S. litura haplotypes. The evolutionary divergence of different strains of Indian-origin S. litura was calculated using the p-distance method in MEGA 11. Neutrality indices, including Tajima’s D, Fu, and Li’s F, was calculated to test the hypothesis of selective neutrality using DnaSPv6. Larval identification relied on the morphological characteristics, while the molecular characterization utilized the mitochondrial cytochrome oxidase I gene with universal primers (LCO1490 and HCO2198). A DNA fragment of approximately 700 bp from mitochondrial COI revealed two different strains (OP420870 and OP117231) infesting sugar beet crops under Indian subtropical conditions. The amplified barcode sequences exhibited variations in both strains, with genetic divergence ranging from 0.0 to 0.79. The strains OP420870 and OP117231 displayed maximum divergence at 0.74 and 0.73, respectively. Interpopulation nucleotide differences (Kxy) and the average number of nucleotide substitutions per site between populations (Dxy) in different states of India were calculated at 336.42 and 0.61, respectively. The pairwise Fst value was 0.63, with an Nm value of 0.15. One of the identified strains of S. litura in this study was also found to be a haplotype. This study provides valuable insights into the genetic characterization of S. litura infesting sugar beet crops in Indian subtropical conditions, contributing to the understanding of its population structure and diversity. The findings enhance our knowledge of S. litura infestations and can aid in the development of effective strategies for pest management and crop protection in sugar beet.