The examined material included males, females and a last-instar nymph found on Japanese spirea, Spiraea japonica, near Hannam station in Seoul. The authors used the collections to establish the species’ presence in South Korea, describe its morphology and breeding host, and add genetic reference data for H. planicornis. The study did not determine the species’ wider distribution within South Korea or whether it occurs elsewhere in the country.

Identification combined external characters with examination of male and female genitalia. This was important because H. planicornis resembles H. merioptera, and current diagnostic characters depend chiefly on differences in genital structures and the relative lengths of antennal segments II and III. The Korean specimens had antennal segment III-to-II length ratios of 0.289–0.303, consistent with the published value for H. planicornis. Their two apically sinuate, unfused endosomal sclerites and parameres also corresponded to published illustrations. A medially bifurcated sclerite depicted in one earlier figure was absent from the Korean material; the authors considered intraspecific variation as a possible explanation and concluded that the specimens represented H. planicornis.

The researchers extracted genomic DNA from abdominal segments IV–VI and legs of alcohol-preserved specimens, prepared libraries with the TruSeq Nano DNA Kit and sequenced them on a NovaSeq X Plus platform. Reads were 151 base pairs long, with 30 million reads per lane. Geneious Prime 2025.1.3 was used for alignment, while MITOS2 and the Proksee web server were used to annotate and visualize the mitochondrial genome. Voucher specimens were deposited in the Insect Biosystematics Laboratory at Seoul National University.

The complete mitochondrial genome of H. planicornis contained 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes and a control region. Its overall GC content was 28.46%. Among the protein-coding genes, GC content ranged from 22.01% for the ATP synthase subunit 8 gene to 36.39% for the cytochrome oxidase subunit I gene. Unlike the other mirid mitochondrial genomes considered in the study, this genome did not have a positive GC skew except in the control region.

For the molecular comparison, the study assembled 14 mitochondrial cytochrome oxidase subunit I sequences, including four from the Korean specimens and ten from GenBank. The analysis used 563 base pairs of the COI region, a neighbor-joining tree and the Kimura 2-parameter model in MEGA 7.0. A male sequence and a female sequence differed from the Canadian H. planicornis sequences by 1.90–1.98%, while a last-instar nymph sequence and another male sequence were nearly identical to the Canadian sequences. The Korean material therefore resolved into two sequence groupings, with one grouping associated with the North American population in the tree and the other occupying a separate branch.

The observations showed that the Korean population was using cultivated Spiraea japonica as a breeding host. Earlier literature cited in the study reported that H. planicornis feeds on plants from 12 angiosperm families and preys on mites, aphids, psyllids, gall midges, eggs and larvae of Chrysomelidae, and eggs of heteropteran and lepidopteran insects. In Korea, the insects were found in narrow artificial landscapes in urbanized areas, rather than in larger available natural habitats such as parks.

The authors did not establish the route or precise geographic source of the introduction. Spiraea japonica is native to Japan and widely cultivated in Europe, while cultivated plants in Korea are imported mainly from Japan and European countries including Germany and the Netherlands. Because no Heterotoma species had been reported from Japan or elsewhere in East Asia, the authors considered introduction from European populations to be likely, presumably with host plants. They also noted that Heterotoma eggs can overwinter and may be transported with host saplings, suggesting that the Korean population might have arrived as eggs. These remain proposed mechanisms rather than directly documented introduction events.

The study is limited by the small number of Korean specimens examined, their concentration on one host plant at a single Seoul locality, and the lack of available European sequences for comparison. Although COI distances below 2% are largely treated as conspecific in prior mirid delimitation studies, the authors note that molecular data for H. planicornis remain limited. The molecular results are consistent with the morphology-based species assignment, but they do not trace the Korean population’s origin. Additional sequence data from H. planicornis populations across geographic regions would be required to examine that origin more precisely.

Subject of Research: First Korean Peninsula record and mitochondrial genome characterization of the introduced mirid Heterotoma planicornis

Article Title: First record of the Heterotoma planicornis ( Hemiptera , Heteroptera , Miridae ), an introduced species in the Korean Peninsula, with characterization of its complete mitochondrial genome

Article References: Oh, M., Cho, S., & Lee, S. (2025). First record of the Heterotoma planicornis (Hemiptera, Heteroptera, Miridae), an introduced species in the Korean Peninsula, with characterization of its complete mitochondrial genome. Deutsche Entomologische Zeitschrift, 72(2), 225-235. https://doi.org/10.3897/dez.72.152970

Image Credits: AI Generated

DOI: 10.3897/dez.72.152970

Keywords: Heterotoma planicornis, Korean Peninsula, South Korea, mitochondrial genome, Miridae, insect distribution, morphological identification, COI phylogeny, Spiraea japonica, introduced species, First, record