Taxonomy of thrips fauna (Thysanoptera: Terebrantia: Thripidae) on ornamental plants in Kerala

Abstract

This belonging to the order Thysanoptera are considered as one of the most economically important group of insect pests worldwide. Some species of thrips act as vectors by transmitting plant viruses. The order comprises about 6288 species of thrips under two suborders viz., Tubulifera and Terebrantia. The suborder Terebrantia primarily consists of phytophagous species in eight families of which the family Thripidae is the largest. The members of Thripidae are widely reported as serious pests of ornamental plants. However, no systematic study has been conducted so far to document the fauna of Thripidae on ornamental plants in Kerala. The present study entitled “Taxonomy of thrips fauna (Thysanoptera: Terebrantia: Thripidae) on ornamental plants in Kerala” was carried out during the period, 2022-23. The research aimed at studying the taxonomy of thrips species of the family Thripidae infesting ornamental plants of Kerala, preparing an illustrated key for the identification of species of Thripidae and generating DNA barcode for cryptic species of thrips collected during the study. Purposive surveys were undertaken in different localities of Kerala covering 43 geographical locations across 14 districts. Thrips specimens were collected from different ornamental plants including flowering trees and the GPS coordinates of the feographical locations as well as the host plants were recorded. The specimens were assigned unique accession numbers and preserved in AGA mix, and then mounted onto permanent slides as per the standard procedure. The slide mounted specimens were used for morphological characterization, and the illustrations of key taxonomic characters and morphometry were made. The amino acid sequences of mitochondrial cytochrome oxidase subunit I (mtCO-I) were analysed for 13 accessions representing eight species. The study recorded 20 species under 14 genera in three subfamilies (Panchaetothripinae, Sericothripinae and Thripinae) from Kerala. The subfamily Thripinae was the most dominant group with 12 species under six genera. The genus Thrips was more diverse with seven species viz., Thrips andrewsi, T. Flavus, T. florum, T. hawaiiensis, T. orientalis, T. paravispinus and T. simplex. The other species in the subfamily includes Chaetanaphothrips signipennis, Echinothrips americanus, Frankliniella schultzei, Microcephalothrips abdominalis and Scirtothrips dorsali. The subfamily Panchaetothripinae recorded seven species under seven genera viz., Astrothrips tumiceps, Caliothrips indicus, Copidothrips octarticulatus, Heliothrips haemorrhoidalis, Retithrips syriacus, Rhipiphorothrips cruentatus and Selenothrips rubrocinctus. The subfamily Sercicothripinae was represented by a single species, Neohydatothrips samayunkur. An illustrated dichotomous taxonomic key for the identification of subfamilies, genera, and species of thrips collected during the study were prepared. A species distribution map was prepared for the Thripidae infesting ornamental plants of Kerala, using Quantum GIS software. A total of 50 plants under 45 genera in 27 families were recorded as hosts for 20 species of thrips species collected in this study. The predominant families of host plants were Asteracea, Oleaceae, Apocynaceae and Rubiaceae. Thrips parvispinus recorded widest host range of 16 host plants in 11 families followed by Microcephalothrips abdominalis (12 host plants in 3 families), Thrips orientalis (9 host plants in 4 families) and Thrips hawaiiensis (8 host plants in 7 families) from Kerala. The DNA barcodes wre generated for eight species viz., Thrips simplex, T. andrewsi, T. parvispinus, T. hawaiiensis, Astrothrips tumiceps, Selenothrips rubrocinctus, Heliothrips haemorrhoidalis and Neohydatothrips samayunkur. A phylogenetic tree was constructed with 27 sequences of different thrips species (13 sequences in the study plus 14 sequences retrieved from NCBI database) and the sequence of aphid, Aphis gossypii as an outgroup in MEGA 11, using UPGMA method. The sequences were submitted to GenBank (NCBI) and BOLD to generate species-specific barcodes. The study identified Echinothrips americanus as a new distribution record for India. The study also identified six new distribution records of thrips for Kerala viz., Neohydatothrips samayunkur, Chaetanaphothrips signipennis, Microcephalothrips abdominalis, Thrips andrewsi, T. Flavus, and T. simplex. The invasive thrips species, T. parvispinus recorded 11 new host plants viz., Cosmos sulphureus, Tabernaemontana sp., Asystasia gangetica, Hibscus rosa sinensis, Canna indica, Rhododendron spp., Spiraea cantoniensis, Antirrhinum majus, Zephyranthes rosea, Uncaria tomentosa and Justicia carnea, suggesting that the species can pose significant threat to ornamental plants of Kerala. The study indicates the need to explore the potential of the above species to become invasive and establish in new habitats. The biotic and abiotic factors that regulate thrips populations on ornamental plants also have to be investigated. Further, thrips fauna associated with other crops of Kerala need to be explored.