Phyllotreta ochripes (Curtis, 1837)

Diagnosis

Phyllotreta ochripes can be recognised in North America and Europe by the following characteristics adapted from Mohr (1966) and Doguet (1994): body 2.0- 2.4 mm; body black with pale stripe or two spots on each elytron; antennae with antennomeres I-III pale in male, with antennomere V two times longer than antennomere VI and somewhat wider; female antennae with antennomeres I-VI pale, antennomere V 1.8 times longer than VI and cylindrical; pale elytral stripes with basal-mesal, sub-basal lateral and apical expansions, pale area occupying most of apical ¼, but not reaching suture or apex; most with legs pale, except femora of hind legs. Here, no other North American Phyllotreta with pale elytral markings has all of the anterior- and mid-legs all pale.

Distribution

We examined 24 specimens of P. ochripes from USA: Illinois, Maryland Michigan, Ohio and Pennsylvania. Specimen data are available through GBIF. org in Douglas (2024). Additional individuals were seen in 29 online iNaturalist citizen-science observations from USA: Indiana, Michigan, Minnesota, Ohio, Pennsylvania, Wisconsin and Canada: Ontario (iNaturalist contributors and iNaturalist 2024). These photos were each identified by iNaturalist contributors as being of P. ochripes and most were confirmed by HD to match P. ochripes and no other North American chrysomelid species. In addition to having pale fore- and mid-legs and elytral markings consistent with only P. ochripes, the distribution of online records was also broadly concordant with that of vouchered specimens (Fig. 3). Additionally, 11 of 29 online records matching P. ochripes were photographed from plants either identified as A. petiolata by the photographers or visually matching A. petiolata. Two additional plants were photographed on plants appearing possibly consistent with A. petiolata, two were photographed on other plant species and the remainder were photographed on non-plant surfaces. Overall, there are strong collections and online evidence of P. ochripes across much of north-eastern USA and in southern Ontario.

We present specimen and photographic evidence of 53 individuals from multiple sites in USA: Maryland, Michigan, Minnesota, Ohio, Pennsylvania, Tennessee, Wisconsin and Canada: Ontario, separated by over 1300 km over six years (earliest observation: 2017, Fig. 2). Photographs on another online citizen-science platform show evidence that this species was already present in USA (Pennsylvania and Tennessee) in 2014 (Moorman 2014, Rossenfeld 2014). These led us to conclude that P. ochripes is established at multiple sites in North America.

Biology

Phyllotreta ochripes has been observed here to make holes fully through all tissue layers of leaves. This is unlike the weevil biological control agent against A. petiolata. Here, Ceutorhyncus scrobicollis Nerensheimer & Wagner (Coleoptera, Curculionidae) causes similar-sized window-pane type damage, where a transparent cuticular layer remains over the damaged area (CABI 2018). Phyllotreta ochripes has been demonstrated to have attraction to allyl isothiocyanate (Tóth et al. 2007), the chemical responsible for the spicy taste of some Brassicaceae.

Notes

The external morphology and genitalia of specimens from USA best matched species concepts of P. ochripes, aligning with European specimens at the CNCI and USNM (Fig. 1). However, the aedeagus of North American specimens had smaller apical concavities than some European specimens. Specimens were all hand-collected from forest understory A. petiolata plants with leaf holes present.

DNA Barcoding Results

Analysis of the DNA-barcoded USA specimens of Phyllotreta through the BOLD Identification Engine resulted in an at least 99.5 % match with some of the 348 publicly available P. ochripes sequences. This specimen shares a BOLD Barcode Index Number (Ratnasingham and Hebert 2013) with two P. ochripes specimens from the country of Georgia for which public data were not available (BOLD: AEH 0075), indicating a maximum p-distance of 0.73 %. However, this bin had a larger p-distance of 3.95 % from a second bin, corresponding to P. ochripes from western Europe. The morphological identification of these specimens as best matching P. ochripes (although with some aedeagal differences), including their presence on Alliaria and the finding that our DNA barcoded specimen closely matched DNA from eastern European specimens, all support the conclusion that the North American specimens are P. ochripes. However, the finding that BOLD has identified a 4 % COI sequence divergence within European P. ochripes may be important. This suggests that more research is needed to determine whether an additional cryptic species is contained within the current concept of P. ochripes.