Species delimitation in asexual insects of economic importance: The case of black scale (Parasaissetia nigra), a cosmopolitan parthenogenetic pest scale insect

Abstract

Asexual lineages provide a challenge to species delimitation because species concepts either have little biological meaning for them or are arbitrary, since every individual is monophyletic and reproductively isolated from all other individuals. However, recognition and naming of asexual species is important to conservation and economic applications. Some scale insects are widespread and polyphagous pests of plants, and several species have been found to comprise cryptic species complexes. Parasaissetia nigra (Nietner, 1861) (Hemiptera: Coccidae) is a parthenogenetic, cosmopolitan and polyphagous pest that feeds on plant species from more than 80 families. Here, we implement multiple approaches to assess the species status of P. nigra, including coalescence-based analyses of mitochondrial and nuclear genes, and ecological niche modelling. Our results indicate that the sampled specimens of P. nigra should be considered to comprise at least two ecotypes (or "species") that are ecologically differentiated, particularly in relation to temperature and moisture. The presence of more than one ecotype under the current concept of P. nigra has implications for biosecurity because the geographic extent of each type is not fully known: some countries may currently have only one of the biotypes. Introduction of additional lineages could expand the geographic extent of damage by the pest in some countries.

Molecular phylogeny of the family Coccidae (Hemiptera, Coccomorpha), with a discussion of their waxy ovisacs

“…Sequences were aligned with mafft v.7 (Katoh & Standley, ). According to the procedures used in previous molecular studies of soft scales (Lin et al ., ; Lin et al ., ,b,c, ), the aligned sequences from each four‐gene region were edited as follows: (i) the presence of stop codons was evaluated in the amino acid translation of the alignments of the two protein‐coding genes ( COI and EF‐1α ); (ii) highly variable regions in the 18S and 28S sequences were excluded; (iii) introns of EF‐1α sequences that could not be aligned unambiguously were deleted (detected using the GT‐AG rule; Roger & Wall, ); and (iv) third codon positions of COI sequences were removed because of nonstationarity (as evaluated by paup * 4.0b10; Swofford, ). Sequences were concatenated using sequencematrix v.1.7.8.…”

“…Coccidae Fallén, , known as ‘the soft scales’, is the third largest family of scale insects, comprising 1183 described species belonging to 169 genera worldwide (as listed in ScaleNet; García Morales et al ., ). The worldwide distribution and polyphagous habit of many species in this family have resulted in a number of coccids becoming agricultural and ornamental pests, such as Coccus hesperidum (Linnaeus), Parasaissetia nigra (Nietner) and Saissetia coffeae (Walker) (Lin et al ., , ).…”

A newly recognised species that has been confused with the global polyphagous pest scale insect, Coccus hesperidum Linnaeus (Hemiptera: Coccomorpha: Coccidae)

“…Considering the level of DNA differentiation, combined with a fixed morphological difference (shape of the apices of dorsal setae), we conclude that specimens with the bluntly rounded dorsal setae represent a distinct species, Coccus praetermissus Lin & Tanaka sp. n., under the species concept for asexual species explained by Lin et al (2017a), that species are independently evolving genetic lineages that are differentiated in additional ways from other such lineages (here, morphologically). YPL00122 MF594276 MF594312 MF579673 MF594365 MF579614 YPL00291 MF594277 MF594313 MF579674 MF594366 MF579615 YPL00465 MF594278 MF594314 MF579675 MF594367 MF579616 YPL00496 MF594279 MF594315 MF579676 MF594368 MF579617 YPL00716 MF594280 MF594316 MF579677 MF594369 MF579618 YPL00732 MF594281 MF594317 MF579678 MF594370 MF579619 C. discrepans (Green) …”

“…Even if males occasionally occur, most reproduction in C. hesperidum s. s. and C. formicarii (a close relative) is asexual, so species concepts based on reproductive isolation are inappropriate. Similarly, phylogenetic species concepts are also inappropriate for asexual lineages because mutation in the absence of sex leads to a pattern of independent lineages and reciprocal monophyly across multiple genes (see discussion in Lin et al 2017a). Here, we apply a species concept for asexual lineages in which species are considered to be independently evolving genetic lineages that are differentiated in additional ways from other such lineages (e.g., ecologically, behaviourally or morphologically) (as per Lin et al 2017a).…”

“…If applying only a general lineage species concept (De Queiroz 1998), these two clades could be argued to represent distinct species. We do not do that here because, currently, specimens in one clade are all from Taiwan and in addition there is not yet evidence of differentiation other than genetic (see arguments for this criterion for asexual lineages in Lin et al 2017a). We exclude the specimens from Taiwan from the formal description of C. praetermissus sp.…”