Barcoding pest species in a biodiversity hot-spot: the South African polyphagous broad-nosed weevils (Coleoptera, Curculionidae, Entiminae)

Abstract

Polyphagous broad nosed weevils (Curculionidae: Entiminae) constitute a large and taxonomically challenging subfamily that contains economically significant agricultural pests worldwide. South Africa is a hot-spot for biodiversity and several species of indigenous and endemic genera of Entiminae have shifted on to cultivated plants, with some being phytosanitary pests. The sporadic pest status of many species (where the species has an occasional economic impact on the agricultural industry, but is not encountered often enough that is is readily recognisable by researchers and agricultural extension workers) and the presence of pest complexes and cryptic species represent an identification challenge to non-specialists. Furthermore, no comprehensive identification tools exist to identify immature stages that may be found in crops/soil. In this paper, a curated barcoding database with 70 COI sequences from 41 species (39 Entiminae, 2 Cyclominae) is initiated, to assist with the complexity of identification of species in this group.

Identifying the Genetic Distance Threshold for Entiminae (Coleoptera: Curculionidae) Species Delimitation via COI Barcodes

“…In the ideal case, the interspecific divergence is larger than intraspecific, as this enables distinguishing species. Some studies have detected barcoding gaps, and some not [ 4 , 25 , 43 , 44 , 45 , 46 ]. Several factors including cryptic species, insufficient sampling, geographical isolation, erroneous taxonomic assignment, incomplete lineage sorting, and homoplasy can all cause exceptionally low inter-GD or high intra-GD, therefore causing the absence of a barcoding gap [ 20 , 36 , 46 , 47 , 48 ].…”

“…In the ideal case, the interspecific divergence is larger than intraspecific, as this enables distinguishing species. Some studies have detected barcoding gaps, and some not [4,25,[43][44][45][46]. Several factors including cryptic species, insufficient sampling, geographical…”

“…Early molecular methods for species delimitation used alloenzyme variability and gene flow (based on Wright's F st statistics), allele frequency, and nuclear gene codominance [9][10][11][12][13]. Currently, the most widely applied method is DNA barcoding, the use of a standard 650 bp fragment of mitochondrial gene cytochrome oxidase I (COI), and has been proven a useful tool in Entiminae taxonomy [4,14,15]. Barcodes have been used to delimit species when other approaches have failed [16].…”

“…Weevils (Coleoptera: Curculionoidea) are one of the most diverse and ubiquitous insect groups in Coleoptera, with more than 62,000 identified species (5800 genera) [ 1 , 2 ], constituting nearly 15% of described Coleoptera [ 3 ]. Entiminae is the largest subfamily in Curculionidae, with more than 12,000 described species within 1280 genera, including many key agricultural pests [ 2 , 4 ]. Most Entiminae are polyphagous, with adults feeding on leaves and young shoots of trees and shrubs, while the larvae feed on roots [ 3 ].…”

“…Characters such as the deciduous mandibular cusps, corbels on the hind tibiae also occur in Brachycerinae (Curculionoidea: Curculionidae) [ 3 ], and many taxa often include cryptic species complexes [ 5 , 6 ]. The morphological differences between closely related species can be so small that even professional taxonomists struggle with identification [ 4 ]. Several factors, including polymorphic species [ 7 ], sexual dimorphism [ 8 ], and immature stages (egg, larva, pupa), may further impede this process.…”