Argopistes sexvittatus and Argopistes capensis (Chrysomelidae: Alticini): Mitogenomics and Phylogeny of Two Flea Beetles Affecting Olive Trees

Abstract

The genus Argopistes (Chrysomelidae: Alticini) is the only group of flea beetles specialized in plant hosts in the family Oleaceae. In southern Africa, Argopistes are often found feeding on African Wild Olive (Olea europaea subsp. cuspidata) and European cultivated olive (O. e. subsp. europaea), and heavy infestations can be devastating to mature trees and compromise the development of young trees. Despite their negative agricultural impact, African Argopistes are an understudied group for which no genetic data were available. We assessed the species diversity of olive flea beetles in the Western Cape province of South Africa, the largest olive-producing region in sub-Saharan Africa, by collecting adult specimens on wild and cultivated olive trees between 2015 and 2017. Argopistes sexvittatus Bryant, 1922 (n = 289) dominated at all sampling sites, and Argopistes capensis Bryant, 1944 (n = 2) was found only once. Argopistes oleae Bryant, 1922, a third species previously reported in the region, was not found. The complete mitogenomes of one A. capensis and two A. sexvittatus (striped and black morphotypes) individuals were sequenced for phylogenetic reconstruction in the context of other 64 species. The two olive flea beetle species form a monophyletic clade with other Argopistes, supporting the hypothesis that the exclusive feeding habit on Oleaceae is an evolutionary adaptation in this genus.

Keywords: DNA barcodes; Olea europaea; South Africa; mitochondrial; olive flea beetles; phylogenetics.

Figure 1

Representative adult specimens of olive flea beetles (Chrysomelidae: Alticini) species found in the Western Cape of South Africa. (A) Argopistes sexvittatus, black morphotype (male); (B) A. sexvittatus, black morphotype (female); (C) A. sexvittatus, black morphotype (male); (D) A. sexvittatus, striped morphotype (male); (E) A. sexvittatus, striped morphotype (female); (F) Argopistes capensis (female). Image credits: Elizabeth Grobbelaar.

Figure 2

(a) Distribution of A. capensis and A. sexvittatus found in African Wild Olive and European cultivated olive trees in the Western Cape province of South Africa. Red dots indicate the approximate location of sampling sites; (b) Study area in the Western Cape; (c) Characteristic leaf damage caused by feeding of olive flea beetles.

Figure 3

Median-joining network of DNA barcode haplotypes of Argopistes sexvittatus (Chrysomelidae: Alticini) (n = 31).

Figure 4

Circular map of the complete mitochondrial genome of Argopistes sexvittatus and A. capensis, here represented by A. sexvittatus AG001. Arrows indicate the direction of gene transcription.

Figure 5

Predicted structure of tRNA^Ser1(TCT) in the complete mitochondrial genomes of (A) A. capensis and (B) A. sexvittatus (striped and black morphotypes).

Figure 6

Usage of start codons found in the complete set of mitochondrial protein-coding genes in 64 species in the tribe Alticini (Coleoptera: Chrysomelidae).

Figure 7

Evolutionary rates (Ka/Ks) of 13 mitochondrial protein-coding genes of 64 species of Alticini (Coleoptera: Chrysomelidae).

Figure 8

Maximum likelihood phylogenetic tree of 64 Alticini species based on 13 mitochondrial protein-coding genes. Nodal support is given as SH-aLRT (%)/ultrafast bootstrap (%); only values >95% are shown. Branch colours represent larval feeding habits: leaf miner—green; external leaf feeder—brown; root feeder—blue; unknown—red. Dashed branches represent possible/unconfirmed/unclear larval feeding habits. * Genus group unclear.

Figure 9

PhyloBayes tree of 64 Alticini species based on 13 mitochondrial protein-coding genes. Nodal support is given as Bayesian Posterior Probability; only values > 0.90 are shown. Branch colours represent larval feeding habits: leaf miner—green; external leaf feeder—brown; root feeder—blue; unknown—red. Dashed branches represent possible/unconfirmed/unclear larval feeding habits. * Genus group unclear.