Research Article
Research Article
Comparative mitogenomic analysis of two earwigs (Insecta, Dermaptera) and the preliminary phylogenetic implications
expand article infoZhi-Teng Chen
‡ Jiangsu University of Science and Technology, Zhenjiang, China
Open Access


The phylogenetic position and inner relationships of Dermaptera remain unresolved despite the numerous efforts using morphological and molecular data. To facilitate the resolution of problems, this study sequenced the complete mitogenome of Apachyus feae de Bormans, 1894 (Apachyidae) and the nearly complete mitogenome of Diplatys flavicollis Shiraki, 1907 (Diplatyidae). The 19,029-bp long mitogenome of A. feae exhibited an extra trnV gene and two control regions in addition to the typical set of 37 genes including 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, and two ribosomal RNA (rRNA) genes. The 12,950-bp long partially sequenced mitogenome of D. flavicollis was composed of 10 and a partial fragment of PCGs, 18 tRNA genes, two rRNA genes, and a control region. Comparative analysis of available earwig mitogenomes revealed variable mitogenomic structure and extensive gene rearrangements in Dermaptera. The preliminary phylogenetic analyses using Bayesian inference and maximum likelihood methods showed identical results, but the limited sampling and different types of molecular data lead to an apparent incongruence with previous phylogenetic studies.


Apachyidae, Dermaptera, Diplatyidae, mitochondrial genome, phylogeny


Dermaptera (earwigs) are a small group of ancient insects in Polyneoptera, with more than 1900 extant species within 11 families known worldwide (Haas 2018). The characteristics such as forceps‐like, unsegmented cerci in the adults of this group are functional in predation, defense, wingfolding and mating (Haas et al. 2000). Most earwigs are free-living and commonly found in damp areas feeding on plant materials, spores, fungi, or insects (Haas 2018). With the exception of Arixeniidae and Hemimeridae, these two families are distinctly epizoic and live non‐parasitically on cavernicolous bats and hamster rats, respectively (Nakata and Maa 1974; Haas and Gorb 2004). The majority of earwigs are oviparous, whereas the epizoic groups are viviparous, i.e., directly giving birth to nymphs. Besides, unusual maternal care behavior is found in all studied earwig species, with the female protecting eggs and first‐instar nymphs (Suzuki et al. 2005; Staerkle and Koelliker 2008).

The extant Dermaptera is traditionally divided into three suborders, i.e., Arixeniina, Hemimerina, and Forficulina (Gullan and Cranston 2010). Arixeniidae and Hemimeridae are sometimes considered to be derived members of Forficulina (nonparasitic Dermaptera) in several studies (Popham 1985; Klass 2001; Engel and Haas 2007). The most recent reclassification of Dermaptera was established by Engel and Haas (2007), which included all extant earwigs in the suborder Neodermaptera. Protodermaptera and Epidermaptera are recognized as two infraorders in Neodermaptera, and Epidermaptera comprises the two epizoic families.

The phylogenetic position of Dermaptera in Insecta and the inner relationship within Dermaptera remain controversial (Beutel et al. 2013). Different research using morphological characteristics or molecular data from nuclear and mitochondrial genes generated different phylogenies of Dermaptera (Wan et al. 2012; Naegle et al. 2016). Wan et al. (2012) sequenced and analyzed the first earwig mitochondrial genome (mitogenome) and investigated the phylogeny of Polyneoptera. To date, Challia fletcheri Burr, 1904 and Euborellia arcanum Matzke & Kocarek, 2015 are the only two complete earwig mitogenomes available in GenBank, and only the mitogenomic structure of C. fletcheri has been analyzed (Wan et al. 2012). To better resolve the phylogeny of earwigs using mitogenomic data, this study sequenced and analyzed two new mitogenomes for Dermaptera. A preliminary phylogenetic tree of Dermaptera is constructed based on the newly sequenced and the known mitogenomic data to provide a basic topology for the relationships among families.

Materials and methods

Sample preparation and DNA extraction

The specimen of Apachyus feae de Bormans, 1894 was collected from Laibin, Guangxi Province of China (24.1402°N, 110.1844°E) in October of 2019; the specimen of Diplatys flavicollis Shiraki, 1907 was collected from Jurong, Jiangsu Province of China (32.1325°N, 119.0743°E) in February of 2020. The specimens were identified by the author, preserved in 100% ethanol, and stored in the Insect Collection of Jiangsu University of Science and Technology (ICJUST). The total genomic DNA of the two earwigs was isolated using the E.Z.N.A. Tissue DNA Kit (Omega Bio-Tek, Inc.) and preserved at −20 °C before the sequencing process.

Sequencing, assembly, annotation, and analysis

The Illumina TruSeq short-insert libraries (size = 450 bp) were constructed using 1 μg of purified DNA fragments and were sequenced by Illumina Hiseq 4000 (Shanghai Biozeron Biotechnology Co., Ltd). Raw reads were filtered prior to assembly; high-quality reads were retained and assembled into contigs by SOAPdenovo2.04 (Luo et al. 2012). The assembled contigs were then aligned to the reference mitogenomes of Dermaptera using BLAST. Subsequently, the aligned contigs (≥80% similarity and query coverage) were arranged according to the reference mitogenomes. Finally, the clean reads were mapped to the assembled draft mitogenomes to fix the wrong bases; gaps were filled using GapFiller v. 2.1.1 ( The mitogenome sequences of A. feae and D. flavicollis were deposited in GenBank under the accession numbers MW291948 and MW291949, respectively. Mitochondrial gene analyses of A. feae and D. flavicollis were compared to four additional species of Dermaptera with available mitogenomes (Table 1). The gene order was compared with Drosophila yakuba Burla, 1954, which was considered to possess the ancestral arthropod mitochondrial gene arrangement (Clary and Wolstenholme 1985).

Table 1.

List of species used in this study.

Infraorder Parvorder Family Species Length (bp) A+T% Accession number
Protodermaptera Diplatyidae *Diplatys flavicollis 12,950 73.5 MW291949
Pygidicranidae Challia fletcheri 20,456 72.6 NC_018538
Epidermaptera Paradermaptera Apachyidae Apachyus feae 19,029 61.2 MW291948
Metadermaptera Anisolabididae Euborellia arcanum 16,087 68.3 KX673196
Eteodermaptera Forficulidae *Eudohrnia metallica 16,324 58.7 KX091853
*Paratimomenus flavocapitatus 15,677 67.4 KX091861
Outgroup Outgroup Outgroup Kamimuria chungnanshana NC_028076

All protein-coding genes (PCGs) and ribosomal RNA (rRNA) genes were identified by homology alignments. Gene boundaries of each PCG were further confirmed by ORF finder ( All transfer RNA (tRNA) genes were predicted and illustrated by the MITOS online server (Bernt et al. 2013). The visual structure of the mitogenomes were depicted using CGView Server ( (Grant and Stothard 2008). Nucleotide composition of each gene and codon usage of PCGs were calculated using MEGA v. 6.0 (Tamura et al. 2013). The composition skew values were calculated by AT-skew = [A – T] / [A + T] and GC-skew = [G – C] / [G + C] formulas (Perna and Kocher 1995). The synonymous substitution rate (Ks) and nonsynonymous substitution rate (Ka) were computed by DnaSP v. 5.10 (Librado and Rozas 2009). Presumed secondary structures in the control regions were predicted by the online tool Tandem Repeats Finder (, DNAMAN v. 6.0.3 and ARWEN ( (Laslett and Canbäck 2008).

Phylogenetic analysis

Nucleotide sequences of PCGs derived from six species of Dermaptera, including A. feae and D. flavicollis sequenced in this study, were used in the phylogenetic analysis (Table 1). The stonefly Kamimuria chungnanshana Wu, 1938 (Plecoptera, Perlidae; GenBank accession no. NC_028076) was used as the outgroup. The 13 PCGs were respectively aligned by MAFFT and concatenated as a combined dataset using SequenceMatrix v. 1.7.8 (Katoh and Standley 2013). The optimal nucleotide substitution models and partitioning schemes for the dataset was determined by PartitionFinder v. 2.1.1 using the Bayesian Information Criterion (BIC) and a greedy search algorithm (Lanfear et al. 2016). Bayesian inferences (BI) and Maximum likelihood (ML) analyses were conducted with the optimal partition schemes. The BI analysis was conducted by MrBayes v. 3.2.7, with 20 million generations sampling every 1000 generations, running one cold chain and three hot chains with a burn-in of 25% trees (Ronquist and Huelsenbeck 2003). TRACER v. 1.5 was used to examine the stability of the results of the BI analysis. The ML analysis was performed by RAxML v. 8.2.12 with 1000 bootstrap replicates (Stamatakis 2014). FigTree v. 1.4.2 was used to adjust and visualize the tree files generated by both BI and ML inferences.


Mitogenome annotation and nucleotide composition

The complete mitogenome of A. feae is a typical double-strand circular molecule with a length of 19,029 bp (Fig. 1). The obtained partial mitogenome of D. flavicollis is 12,950 bp in length (Fig. 1). The completely sequenced three mitogenomes of Dermaptera range in size from 16,087 bp in E. arcanum to 20,456 bp in C. fletcheri. In the mitogenome of A. feae, an extra trnV gene and two control regions are found in addition to the standard set of 37 genes (13 PCGs, 22 tRNA genes and two rRNA genes) (Table 2). In the partial mitogenome of D. flavicollis, 10 and a partial fragment of PCGs, 18 tRNA genes, two rRNA genes, and a control region are annotated (Table 3). In A. feae, there are 56 overlapping nucleotides located in three pairs of neighboring genes, and the longest overlap is 41-bp long and located between trnT and ND4L (Table 2). A total of 296 intergenic nucleotides (IGNs) are dispersed in 19 locations for A. feae. In D. flavicollis, 17 overlapping nucleotides and 504 IGNs are found, including a 227-bp long IGN between trnS2 (UCN) and ND1 (Table 3).

Table 2.

Mitochondrial genome structure of Apachyus feae.

Gene Position (bp) Size (bp) Direction Intergenic nucleotides Anti- or start/stop codons A+T%
trnIle (I) 1–62 62 Forward 0 GAT 64.5
trnGln (Q) 171–240 70 Reverse 108 TTG 65.7
trnMet (M) 257–326 70 Forward 16 CAT 61.4
ND2 328–1347 1020 Forward 1 ATT/TAA 62.3
trnTrp (W) 1350–1415 66 Forward 2 TCA 63.6
trnCys (C) 1408–1474 67 Reverse −8 GCA 62.7
trnTyr (Y) 1476–1539 64 Reverse 1 GTA 67.2
COX1 1540–3075 1536 Forward 0 ATG/TAG 58.1
trnL2 (UUR) 3081–3147 67 Forward 5 TAA 62.7
COX2 3148–3831 684 Forward 0 ATG/TAG 58.0
trnLys (K) 3832–3901 70 Forward 0 CTT 61.4
trnAsp (D) 3903–3971 69 Forward 1 GTC 79.7
ATP8 3972–4133 162 Forward 0 GTG/TAG 57.4
ATP6 4127–4807 681 Forward −7 ATG/TAG 58.1
COX3 4813–5607 795 Forward 5 TTG/TAA 56.7
trnGly (G) 5620–5680 61 Forward 12 TCC 78.7
ND3 5681–6034 354 Forward 0 ATG/TAG 56.8
trnAla (A) 6036–6099 64 Forward 1 TGC 45.3
trnVal2 (GUU) 6109–6168 60 Reverse 9 AAC 60.0
trnGlu (E) 6177–6238 62 Forward 8 TTC 74.2
trnArg (R) 6241–6301 61 Forward 2 TCG 68.9
trnSer1 (AGN) 6303–6363 61 Forward 1 GCT 70.5
trnAsn (N) 6385–6448 64 Reverse 21 GTT 58.5
trnPhe (F) 6533–6598 66 Forward 84 GAA 77.3
ND5 6599–8347 1749 Reverse 0 ATG/TAA 57.5
trnHis (H) 8348–8414 67 Reverse 0 GTG 61.2
ND4 8415–9795 1381 Reverse 0 ATG/T− 59.9
ND4L 9755–10045 291 Reverse −41 ATG/TAA 60.8
trnThr (T) 10,053–10,115 63 Forward 7 TGT 73.0
trnPro (P) 10,116–10,179 64 Reverse 0 TGG 64.1
ND6 10,182–10,730 549 Forward 2 ATT/TAA 62.8
CYTB 10,741–11,818 1078 Forward 10 ATT/T– 58.2
trnSer2 (UCN) 11,819–11,887 69 Forward 0 TGA 73.9
CR2 11,888–15,172 3285 Forward 0 59.5
ND1 15,173–16,120 948 Reverse 0 ATG/TAG 62.3
trnLeu1 (CUN) 16,121–16,187 67 Reverse 0 TAG 70.1
rrnL 16,188–17,467 1280 Reverse 0 67.9
trnV1 (GUA) 17,468–17,534 67 Reverse 0 TAC 67.2
rrnS 17,535–18,273 739 Reverse 0 66.0
CR1 18,274–19,029 756 Forward 0 74.2
Table 3.

Mitochondrial genome structure of Diplatys flavicollis.

Gene Position (bp) Size (bp) Direction Intergenic nucleotides Anti- or start/stop codons A+T%
COX1 (partial) 1–310 310 Forward 0 ?/TAA 64.5
trnLys (K) 398–463 66 Forward 87 CTT 68.2
trnAsp (D) 464–532 69 Forward 0 GTC 87.0
ATP8 533–706 174 Forward 0 ATT/TAG 75.9
ATP6 700–1377 678 Forward −7 ATG/TAA 72.5
COX3 1388–2200 813 Forward 10 ATT/TAA 68.5
trnGly (G) 2222–2286 65 Forward 21 TCC 75.4
ND3 2287–2637 351 Forward 0 ATT/TAA 74.3
trnAla (A) 2660–2724 65 Forward 22 TGC 77.6
trnAsn (N) 2736–2803 68 Forward 11 GTT 78.5
trnGlu (E) 2815–2879 65 Forward 11 TTC 77.5
trnTyr (Y) 2895–2969 75 Forward 15 GTA 80.0
trnCys (C) 2985–3051 67 Forward 15 GCA 79.7
trnGln (Q) 3059–3127 69 Forward 7 TTG 76.8
CR 3128–3719 592 Forward 0 82.6
trnSer1 (AGN) 3720–3784 65 Reverse 0 GCT 69.2
trnArg (R) 3785–3852 68 Reverse 0 TCG 78.3
trnPhe (F) 3854–3925 72 Reverse 1 GAA 90.5
ND5 3928–5673 1746 Reverse 2 ATC/TAA 71.5
trnHis (H) 5674–5739 66 Reverse 0 GTG 83.6
ND4 5747–7099 1353 Reverse 7 ATC/TAA 72.0
ND4L 7090–7386 297 Reverse −10 ATT/TAA 74.3
trnThr (T) 7394–7464 71 Forward 7 TGT 74.6
trnPro (P) 7465–7537 73 Reverse 0 TGG 80.0
ND6 7540–8043 504 Forward 2 ATT/TAG 76.4
CYTB 8056–9198 1143 Forward 12 ATG/TAG 69.8
trnSer2 (UCN) 9246–9318 73 Forward 47 TGA 77.0
ND1 9546–10487 942 Reverse 227 ATT/TAA 69.9
trnLeu1 (CUN) 10,488–10,554 67 Reverse 0 TAG 79.1
rrnL 10,555–11,918 1364 Reverse 0 76.1
trnVal (V) 11,919–11,990 72 Reverse 0 TAC 72.2
rrnS 11,991–12,950 960 Reverse 0 76.9
Figure 1. 

Mitochondrial maps of Apachyus feae and Diplatys flavicollis. Genes outside the map are transcribed clockwise, whereas those inside the map are transcribed counterclockwise. Names and other details of the genes are listed in Tables 2 and 3. The inside circles show the GC content and the GC skew. GC content and GC skew are plotted as the deviation from the average value of the entire sequence.

The mitogenomes of A. feae and D. flavicollis are biased toward A and T nucleotides (61.2% and 73.5%, respectively), which is consistent with other earwigs (Table 1). The A+T contents were also rich in each mitochondrial gene, showing the highest in trnD of A. feae and trnF of D. flavicollis.

Gene rearrangement

In the sequenced earwigs, no PCG rearrangement are found (Fig. 2). In A. feae, most tRNA genes in the gene cluster trnA-R-N-S1-E-F are rearranged, and an extra trnV is present in the gene cluster. In D. flavicollis, the gene cluster trnA-R-N-S1-E-F is also rearranged and incorporates trnY, trnC and trnQ from other locations. In C. fletcheri, trnI, trnC, trnY, trnQ, and trnE are rearranged (Wan et al. 2012). In E. arcanum, trnQ, trnC, trnY, trnR, and trnS1 are rearranged, and trnY is lost. In E. metallica and P. flavocapitatus, both trnR and trnS1 are absent. These tRNA rearrangements mainly occur in the trnA-R-N-S1-E-F gene cluster. The two rRNA genes are located in the same location for all sequenced earwigs; however, they are variable in size interspecifically. In addition to the tRNA rearrangements, the control region of D. flavicollis transfers to the new location between ND3 and ND5; an extra control region is also found in A. feae and C. fletcheri (Wan et al. 2012).

Figure 2. 

Mitochondrial gene arrangement of six earwigs in comparison with Drosophila yakuba.

Protein-coding genes (PCGs)

All PCGs of A. feae are annotated, whereas ND2, COX2, and partial COX1 of D. flavicollis are not sequenced. The PCGs of A. feae are similar in size to those of D. flavicollis and other earwigs. Most PCGs of A. feae and all PCGs of D. flavicollis utilize the standard ATN start codon (ATT, ATC, and ATG), whereas ATP8 and COX3 of A. feae start with special start codons (GTG and TTG, respectively) (Tables 2, 3). Most PCGs of A. feae and all PCGs of D. flavicollis have the complete termination codon TAN (TAA or TAG), whereas ND4 and CYTB of A. feae end with an incomplete stop codon T (Tables 2, 3). The relative synonymous codon usage (RSCU) values were calculated for the six earwig mitogenomes (Fig. 3). The most frequently used codon is TCT (Ser) for A. feae, TTG (Leu) for E. metallica, TTA (Leu) for D. flavicollis, C. fletcheri, E. arcanum, and P. flavocapitatus.

Figure 3. 

Relative synonymous codon usage (RSCU) of PCGs in six species of earwigs.

The ratio of Ka/Ks was calculated for each PCG of the six earwig mitogenomes to evaluate the evolutionary rates of the PCGs (Fig. 4). The results showed that COX1 of E. metallica has the highest evolutionary rate, followed by ND5 of A. feae and ND2 of P. flavocapitatus, whereas COX1 of A. feae and E. arcanum appear to be the lowest. The genes with ratios of Ka/Ks above 1 are evolving under positive selection. Other genes with ratios of Ka/Ks below 1 are expected to evolve under purifying selection.

Figure 4. 

Evolutionary rates of PCGs in six species of earwigs. The bar indicates each gene’s Ka/Ks value.

Transfer RNA (tRNA) genes

The typical set of 22 tRNA genes and an extra trnV gene are detected in the mitogenome of A. feae (Fig. 5). In D. flavicollis, 18 tRNA genes are recognized and the four tRNA genes trnI, trnM, trnW, trnL are absent due to the incomplete sequencing of 5´ end (Fig. 6). In other sequenced earwigs, C. fletcheri has all 22 tRNA genes (Wan et al. 2012), E. arcanum lacks trnY, and E. metallica and P. flavocapitatus lack trnR and trnS1. Individual tRNA gene of the two newly sequenced mitogenomes range in size from 60 to 75 bp; the longest tRNA gene is trnY in D. flavicollis, and the shortest tRNA gene is the extra trnV in A. feae. In the mitogenomes of A. feae and D. flavicollis, most of the tRNA genes exhibit cloverleaf secondary structures, but the dihydrouridine (DHU) arm is lost for the extra trnV of A. feae and is reduced for trnS1 of both species. The anticodons of the tRNA genes were identical among the earwigs. In the tRNA genes of A. feae and D. flavicollis, a total of 48 and 25 mismatched base pairs are respectively recognized and all of them are G-U pairs.

Figure 5. 

Secondary structures of tRNA genes in the mitogenome of Apachyus feae. Mismatched base pairs are indicated by red circles; reduced arms are indicated by red arrowheads.

Figure 6. 

Secondary structures of tRNA genes in the mitogenome of Diplatys flavicollis. Mismatched base pairs are indicated by red circles; reduced arms are indicated by red arrowheads.

Ribosomal RNA (rRNA) genes

Two rRNA genes are consistently found in all sequenced mitogenomes. Locations of the two rRNA genes are conserved among earwig species and similar to D. yakuba, but the lengths are variable. In A. feae, the large ribosomal RNA (rrnL) gene is 1280 bp in length with an A+T content of 67.9%; the small ribosomal RNA (rrnS) gene is 739 bp with an A+T content of 66.0%. In D. flavicollis, the rrnL gene is 1364 bp with an A+T content of 76.1%; the rrnS gene is 960 bp with an A+T content of 76.9%.

Control region

Two putative control regions (CRs) are found in the mitogenomes of A. feae, E. metallica and P. flavocapitatus. The CR1 of A. feae is 756 bp and located after rrnS, containing a stem-loop (SL) structure and a poly-[TA]n like stretch (Fig. 7). The CR2 of A. feae is 3285-bp long and located between trnS2 (UCN) and ND1, being composed of five SL structures and three copies of tandem repeats. The CR of D. flavicollis is 592 bp and located between trnQ and trnS1, comprising two and partial copies of tandem repeats, two tRNA-like structures, and a poly-[T]n stretch (Fig. 8). In C. fletcheri, the 1816-bp long CR1 contains a SL structure and two regions of tandem repeats; the entire 2856-bp long CR2 comprises 21.1 copies of tandem repeats (Fig. 9). The CR of E. arcanum is 686 bp in size, containing a SL structure, a poly-[TA]n stretch and a tandem repeats region (Fig. 9). The 891-bp long CR of E. metallica comprises four SL structures (Fig. 9). The CR of P. flavocapitatus is short, 227-bp in size, and contains one SL structure (Fig. 9).

Figure 7. 

Predicted structural elements in the control regions of Apachyus feae.

Figure 8. 

Predicted structural elements in the control region of Diplatys flavicollis.

Figure 9. 

Predicted structural elements in the control regions of Challia fletcheri, Euborellia arcanum, Eudohrnia metallica, and Paratimomenus flavocapitatus.

Phylogenetic analyses

The phylogenetic analyses use the nucleotide sequences of six available earwig mitogenomes to investigate the mitochondrial phylogenetic relationships within Dermaptera. The two phylogenetic trees using BI and ML analyses generated identical topological structures for Dermaptera (Fig. 10). The monophyly of Forficulidae is supported with high values. Diplatyidae is recovered as the sister group of Anisolabididae and their combined clade is grouped with Pygidicranidae. Apachyidae is supported as the sister group to other sequenced families. Monophyly of the two infraorders Protodermaptera and Epidermaptera cannot be supported by either analysis. The three parvorders Paradermaptera, Metadermaptera, and Eteodermaptera are each represented by single family and their relationship was recovered as Paradermaptera + (Eteodermaptera + Metadermaptera).

Figure 10. 

Phylogenetic relationships within Dermaptera inferred by Bayesian inference and maximum likelihood analysis. Numbers at the nodes are posterior probabilities (left) and bootstrap values (right). The family names are listed after the species. Infraorders and parvorders are indicated below each family name.


This study sequenced and comparatively analyzed two earwig mitogenomes with other available public data. The mitogenomes of A. feae and D. flavicollis were slightly smaller in size than that of C. fletcheri (20,456 bp) (Wan et al. 2012). Unlike most other insects (Wei et al. 2010), the A. feae mitogenome has both negative AT-skew and GC-skew values as in E. metallica and P. flavocapitatus, whereas D. flavicollis exhibits negative AT-skew and positive GC-skew values as in C. fletcheri (Wan et al. 2012) and E. arcanum. The number of mitochondrial genes and control regions were variable in Dermaptera, either with the addition or loss of several tRNA genes. In other four completely or partially sequenced mitogenomes of Dermaptera, the presence of typical 37 genes and two elongated control regions is found in C. fletcheri (Wan et al. 2012), the lack of trnY is found in E. arcanum, and the absence of trnR and trnS1 (AGN) occurs in both E. metallica and P. flavocapitatus. The presence of an elongated control region or an extra control region is temporarily considered a common phenomenon in earwig mitogenomes. The elongated non-coding regions in Dermaptera (as found in A. feae and C. fletcheri) could contribute to the frequently large mitogenomic size (Wan et al. 2012), which is also common in other insect orders, such as in Plecoptera (Chen and Du 2017). Multiple IGNs were present in all available mitogenomes of Dermaptera, indicating a loose mitogenomic structure for the earwigs. No PCG rearrangements were found in all sequenced earwigs (Fig. 2). The PCGs and rRNA genes of Dermaptera seemed conserved in arrangements, but this should be confirmed by more mitogenomic data. Rearrangement of tRNA genes were detected in all sequenced earwig species (Fig. 2). The rearrangements concerning tRNA genes occur very frequently in the sequenced earwigs and mainly focus on the trnA-R-N-S1-E-F gene cluster, which is similar to the arrangement in Lepidoptera (Cao et al. 2012; Gong et al. 2012; Wang et al. 2014; Park et al. 2016). Extensive mitochondrial rearrangement events are expected to occur in other unsequenced earwigs.

The Ka/Ks calculation revealed the fast-evolving COX1 and slow-evolving CYTB in earwigs. The fast-evolving genes are potential candidates as molecular markers for future genetic studies of Dermaptera. Among the very few molecular studies of Dermaptera, Naegle et al. (2016), Stuart et al. (2019), and Kirstová et al. (2020) supported the efficiency of COX1 gene in species delimitation and phylogenetic reconstruction. In tRNA genes, reductions of trnS1 DHU arms was very common in other metazoans (Garey and Wolstenholme 1989). The shortened DHU arm of trnS1 found in A. feae and D. flavicollis was also found in C. fletcheri but absent in other earwigs (Wan et al. 2012).

The control regions of Dermaptera were highly variable in size, location, and secondary structures. The putative structural elements in the CRs included SL structure, poly-[TA]n like stretch, tandem repeats, tRNA-like structure and poly-[T]n stretch, and they were highly variable in both size and numbers, which implied that the earwig mitogenomes are likely to be regulated in apparent different ways during the mitogenomic replication and transcription processes.

In the phylogenetic analyses, the monophyly of Forficulidae was supported with high values The basal phylogenetic position of Apachyidae was also recovered based on nuclear single-copy genes (Wipfler et al. 2020). However, the current relationship between the five earwig families is entirely incongruent with all previous phylogenetic studies using either morphological data, other types of molecular markers, or combined data (Haas 1995; Guillet and Vancassel 2001; Haas and Kukalova-Peck 2001; Colgan et al. 2003; Jarvis et al. 2005; Kocarek et al. 2013; Naegle et al. 2016; Wipfler et al. 2020). The preliminary phylogenetic analyses in current study included very few representatives from only five earwig families and thus insufficient for comparison with previous studies. The currently available mitogenomic data could not resolve the relationship within Dermaptera. More comprehensive sampling and sequencing work are necessary to clarify the mitogenomic features and mitogenomic phylogeny of Dermaptera.


The mitochondrial genomes of A. feae and D. flavicollis were sequenced, analyzed, and compared with other sequenced earwigs. The phylogenetic reconstructions with BI and ML methods generated identical topology but differed from previous phylogenetic studies using morphological data or other molecular markers. Due to the limited sample size, the relationships found here must be treated with caution. More mitogenomes should be obtained in future works to resolve the phylogeny of earwigs.


This work was supported by the Natural Science Foundation of Jiangsu Province (grant no. BK20201009) and the Start-up Funding of Jiangsu University of Science and Technology (grant no. 1182931901). The author thanks the editor and reviewers for valuable comments and manuscript improvement.


  • Bormans ADE (1894) Viaggio di Leonardo Fea in Birmaniae regioni vicne. LXI. Dermapters (2nd Partie). Annali di Museo Civico di Storia Naturale di Giacomo Doria 14(2): 371–409.
  • Burr M (1904) Observations on the Dermatoptera, including revisions of several genera, and descriptions of new genera and species. Transactions of the American Entomological Society 52(2): 277–322.
  • Bernt M, Donath A, Jühling F, Externbrink F, Florentz C, Fritzsch G, Pütz J, Middendorf M, Stadler PF (2013) MITOS: improved de novo metazoan mitochondrial genome annotation. Molecular Phylogenetics and Evolution 69(2): 313–319.
  • Beutel R, Wipfler B, Gottardo M, Dallai R (2013) Polyneoptera or “Lower Neoptera”-New light on old and difficult phylogenetic problems. Atti Accademia Nazionale Italiana di Entomologia 61: 113–142.
  • Cao YQ, Ma C, Chen JY, Yang DR (2012) The complete mitochondrial genomes of two ghost moths, Thitarodes renzhiensis and Thitarodes yunnanensis: the ancestral gene arrangement in Lepidoptera. BMC Genomics 13(1): 1–13.
  • Chen ZT, Du YZ (2017) First mitochondrial genome from Nemouridae (Plecoptera) reveals novel features of the elongated control region and phylogenetic implications. International Journal of Molecular Sciences 18(5): e996.
  • Grant JR, Stothard P (2008) The CGView server: a comparative genomics tool for circular genomes. Nucleic Acids Research 36: 181–184.
  • Garey JR, Wolstenholme DR (1989) Platyhelminth mitochondrial DNA: evidence for early evolutionary origin of a tRNAserAGN that contains a dihydrouridine arm replacement loop, and of serine-specifying AGA and AGG codons. Journal of Molecular Evolution 28: 374–387.
  • Gullan PJ, Cranston PS (2010) The Insect: an Outline of Entomology, 4th edn. John Wiley & Sons, Oxford, 565 pp.
  • Guillet S, Vancassel M (2001) Dermapteran life-history evolution and phylogeny with special reference to the Forficulidae family. Evolutionary Ecology Research 3: 477–486.
  • Gong YJ, Shi BC, Kang ZJ, Zhang F, Wei SJ (2012) The complete mitochondrial genome of the oriental fruit moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae). Molecular Biology Reports 39(3): 2893–2900.
  • Haas F, Kukalová-Peck J (2001) Dermaptera hindwing structure and folding: new evidence for familial, ordinal and superordinal relationships within Neoptera (Insecta). European Journal of Entomology 98: 445–510.
  • Jarvis KJ, Haas F, Whiting MF (2005) Phylogeny of earwigs (Insecta: Dermaptera) based on molecular and morphological evidence: reconsidering the classification of Dermaptera. Systematic Entomology 30(3): 442–453.
  • Katoh K, Standley DM (2013) MAFFT multiple sequence alignment software version 7: improvements in performance and usability. Molecular Biology and Evolution 30: 772–780.
  • Klass KD (2001) The female abdomen of the viviparous earwig Hemimerus vosseleri (Insecta: Dermaptera: Hemimeridae), with a discussion of the postgenital abdomen of Insecta. Zoological Journal of the Linnean Society 131: 251–307.
  • Kirstová M, Kundrata R, Kočárek P (2020) Molecular phylogeny and classification of Chelidurella Verhoeff, stat. restit. (Dermaptera: Forficulidae). Insect Systematics and Evolution 52(3): 335–371.
  • Lanfear R, Frandsen PB, Wright AM, Senfeld T, Calcott B (2016) PartitionFinder 2: new methods for selecting partitioned models of evolution for molecular and morphological phylogenetic analyses. Molecular Biology and Evolution 34: 772–773.
  • Luo RB, Liu BH, Xie YL, Li Z, Huang W, Yuan J, He G, Chen Y, Pan Q, Liu Y, Tang J, Wu G, Zhang H, Shi Y, Liu Y, Yu C, Wang B, Lu Y, Han C, Cheung DW, Yiu SM, Peng S, Zhu XQ, Liu G, Liao X, Li Y, Yang H, Wang J, Lam TW, Wang J (2012) SOAPdenovo2: an empirically improved memory-efficient short-read de novo assembler. GigaScience 1: 1–18.
  • Matzke D, Kocarek P (2015) Description and biology of Euborellia arcanum sp. nov., an alien earwig occupying greenhouses in Germany and Austria (Dermaptera: Anisolabididae). Zootaxa 3956(1): 131–139.
  • Naegle MA, Mugleston JD, Bybee SM, Whiting MF (2016) Reassessing the phylogenetic position of the epizoic earwigs (Insecta: Dermaptera). Molecular Phylogenetics and Evolution 100: 382–390.
  • Nakata S, Maa TC (1974) A review of the parasitic earwigs (Dermaptera: Arixeniina; Hemimerina). Pacific Insects 16: 307–374.
  • Park JS, Kim MJ, Jeong SY, Kim SS, Kim I (2016) Complete mitochondrial genomes of two gelechioids, Mesophleps albilinella and Dichomeris ustalella (Lepidoptera: Gelechiidae), with a description of gene rearrangement in Lepidoptera. Current Genetics 62(4): 809–826.
  • Perna NT, Kocher TD (1995) Patterns of nucleotide composition at fourfold degenerate sites of animal mitochondrial genomes. Journal of Molecular Evolution 41: 353–358.
  • Stuart OP, Binns M, Umina PA, Holloway J, Severtson D, Nash M, Heddle T, van Helden M, Hoffmann AA (2019) Morphological and molecular analysis of Australian earwigs (Dermaptera) points to unique species and regional endemism in the Anisolabididae family. Insects 10(3): e72.
  • Suzuki S, Kitamura M, Matsubayashi K (2005) Matriphagy in the hump earwig, Anechura harmandi (Dermaptera: Forficulidae), increases the survival rates of the offspring. Journal of Ethology 23(2): 211–213.
  • Shiraki T (1907) Neue Blattiden und Forficuliden Japans. Transactions of the Sapporo Natural History Society 2: 103–111.
  • Tamura K, Stecher G, Peterson D, Filipski A, Kumar S (2013) MEGA6: Molecular Evolutionary Genetics Analysis version 6.0. Molecular Biology and Evolution 30: 2725–2729.
  • Wipfler B, Koehler W, Frandsen PB, Donath A, Liu S, Machida R, Misof B, Peters RS, Shimizu S, Zhou X, Simon S (2020) Phylogenomics changes our understanding about earwig evolution. Systematic Entomology 45(3): 516–526.
  • Wu CF (1938) The stoneflies of China (Order Plecoptera). Peking Natural History Bulletin 13(1): 53–87.
  • Wang W, Meng ZQ, Shi FX, Li F (2013) Advances in comparative studies of Lepidoptera (Arthropoda: Insecta). Chinese Science Bulletin 30: 3017–3029.
  • Wan X, Kim MI, Kim MJ, Kim I (2012) Complete mitochondrial genome of the free-living earwig, Challia fletcheri (Dermaptera: Pygidicranidae) and phylogeny of Polyneoptera. PLoS ONE 7: e42056.
login to comment