Diversity in thrips palmi: Exploration of genetic and ecological heterogeneity

Thrips palmi Karny (Thysanoptera: Thripidae), an impactful pest in Southeast and East Asia, spread to Africa, Oceania, and the Americas in the past decades. Besides being a principal pest of vegetables, legumes, fibre, and ornamental crops, T. palmi serves as the vector for several plant viruses that cause substantial economic losses. The impact of intraspecies heterogeneity in the evolution of pesticide-resistant, host-specific, and geo-ecological strains is known for several thrips species. The present study aims to explore the genetic basis of the intraspecies heterogeneity of T. palmi populations if any. The genetic diversity within T. palmi has been recognized by 35 microsatellite markers, sequencing mitochondrial cytochrome oxidase subunit I (mtCOI), and international transcribed spacer 2 (ITS-2) markers. A total of 93 populations were collected from diverse ecological niches of India. Out of which 20 populations were identified as T. palmi. A total of 286 mtCOI and 66 ITS2 sequences of T. palmi originating from different parts of the world including the sequences generated in this study were considered to ascertain the genetic diversity. All the collected Indian populations are clustered into two distinct ancestries in Structure analysis, with a predominant inclination towards ancestry I. A high intraspecific diversity of global populations of T. palmi up to 19% based on mtCOI sequences and 15% in ITS2 sequences is indicative of the presence of cryptic species. Phylogenetic analyses and haplotype networking clustered the global population of T. palmi into five lineages. Restricted gene flow was anticipated among the major lineages of T. palmi. The results suggest the existence of reproductively isolated populations due to potential geographical barriers. Excess of rare alleles suggested a recent selective sweep or population expansion after a recent bottleneck that seeks a further evolutionary understanding of T. palmi population globally, and its introduction and ecesis in new areas. The study proposes that T. palmi populations across the globe represent a species complex with broader genetic boundaries and reproductive isolation that suggest further taxonomical appraisal.