Plutella xylostella (Linnaeus, 1758)

Landry, Jean-Francois & Hebert, Paul DN, 2013, Plutella australiana (Lepidoptera, Plutellidae), an overlooked diamondback moth revealed by DNA barcodes, ZooKeys 327, pp. 43-63 : 52-53

Plutella xylostella (Linnaeus, 1758) Figs 10-16, 18, 20, 22, 24, 26, 28, 30, 32

Plutella karsholtella Baraniak, 2003: 31. New synonymy. Type locality: Canary Islands, Tenerife. Holotype in ZMUC. Barcoded.

Remarks.

Baraniak (2003) described Plutella karsholtella from three female specimens based on minor differences in genitalia from Plutella xylostella . The main difference (given in his diagnosis) is that the distal portion of the ductus bursae has a curve at the level of the antrum when viewed laterally. There are two drawings of the female genitalia in Baraniak (2003), one showing the ventral aspect, the other in lateral aspect, but it is not indicated what preparations or specimens they are based on, nor whether both were drawn from the same specimen. Considering that the two paratypes are from localities widely distant from the type locality (one is from northwestern Turkey, the other from Greece) and that the difference from Plutella xylostella is slight, it would have been important to indicate the stability of this trait. The similarity of the holotype barcode with a common haplotype of Plutella xylostella and the single minor difference in female genitalia (male genitalia unknown) suggest that it is synonymous with the latter and we consider it so here. We omit the suite of other previously well-established junior synonyms of Plutella xylostella , which can be found in Robinson and Sattler (2001).

The colouration of Plutella xylostella has been characterized as variable, with paler individuals in xeric regions ( Robinson and Sattler 2001). Our examination of many specimens from Asia, Australia, Europe, and North America showed that much of the forewing variation appears restricted to females. Males are relatively constant in having the typical forewing pattern with a strongly defined, ochre or cream-coloured, scalloped dorsal fascia contrasting markedly with the brown anterior two-thirds. Females display significant individual variation deviating from this pattern, from a dorsal fascia that is more subdued to one that is indistinct or nearly lacking (Figs 12-16).

In a taxonomic review of Hawaiian Plutella , Robinson and Sattler (2001) described two morphologically indistinguishable 'host races’ of Plutella xylostella , reared from larvae consuming the fruits (rarely the leaves) of caperbush ( Capparis , Capparaceae ). The recognition of two separate races with the same, albeit unusual, host was geographical, each being restricted to an island: 'host-race 1' found on Oahu was characterized as having a forewing pattern typical of "faded or at best weakly indicated" Plutella xylostella ; whereas 'host-race 2' found on the big island of Hawaii was described as "unusual very pale ( …) white to cream with faded yellow markings". They did not find significant genitalia differences from typical Plutella xylostella , which also occurs in the Hawaiian archipelago where it has been reared from several Brassicaceae . The colour differences that they describe for the host races appear to fall within the known variation of Plutella xylostella elsewhere and may not be diagnostically significant.

At least one of these Hawaiian races was included in a previous study of mtDNA variation in Plutella xylostella (as undescribed Plutella ‘UPA’ by Chang et al. (1997)). However, the sequenced specimens were without host plant record (not reared) and no vouchers were retained so their identity cannot be verified. Their short sequences (GenBank accession numbers AF019041 for Plutella ‘UPA’ and AF019042 for Plutella ‘UPB’) overlap the 3' half of the barcode region and, when compared to our results, are more than 10% divergent from the australiana–xylostella cluster, suggesting no conspecificity with either.