Identification and analysis of the complete mitochondrial genome of Thaumetopoea pityocampa (Lepidoptera: Notodontidae)

Abstract The mitochondrial genome (mitogenome) provides important information for phylogenetic analysis and understanding evolutionary origins. Thaumetopoea pityocampa is a forest pest that harms nearly all cedar and pine species. In this study, the T. pityocampa mitochondrial genome was sequenced, assembled, and annotated. The sequence length of the genome was found to be 15,737 bp, containing 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes, and an A + T-rich region compared with the genomes of other lepidopterans. The overall nucleotide composition is: 37.3% T, 40.5% A, 14.6% C, and 7.6% G, demonstrating an AT bias (A + T: 77.8%). Our phylogenetic tree analysis results showed that T. pityocampa and Ochrogaster lunifer were the most similar species, with the closest evolutionary distance. The mitogenome sequence determined in this study will contribute to improved understanding of Notodontidae evolution.

Thaumetopoea pityocampa; mitochondrial genome; phylogenetic analysis Lepidoptera, which contains butterflies and moths, is the second largest order of insects, surpassed only by Coleoptera. Noctuoidea is among the largest superfamilies within Lepidoptera, with almost 42,400 described species. Thaumetopoea pityocampa (Lepidoptera: Notodontidae) is a pest that consumes the needles of conifers such as Cedrus, Pinus, and Pseudotsuga (Colacci et al. 2018). Besides damaging forest production, the setae of T. pityocampa are also a threat to human and animal health because they contain allergens such as Tha p 1 and Tha p 2 (Rebollo et al. 2002;Vega et al. 2011;Rodriguez-Mahillo et al. 2012;Kaszak et al. 2015;Berardi et al. 2017). Insect genomic information improves our understanding of various aspects of pests such as their physiology, biochemistry, reproduction, migration, and tolerance to extreme environments. The T. pityocampa genome is 537 Mb in length; de novo transcriptomic analysis of two phenologically divergent populations has identified 9625 unigenes while 29,701 bona fide unigenes found in samples from different developmental stages (Gschloessl et al. 2014;Gschloessl et al. 2018). Although mitochondrial gene fragments of T. pityocampa have been sequenced and compared with those from other species or different locations, complete mitochondrial genome sequencing remains to be performed and is necessary for phylogenetic and evolutionary research (Kerdelhue et al. 2009;Rousselet et al. 2010). In this study, we report the complete mitochondrial genome of T. pityocampa.
T. pityocampa eggs used for studying were collected in October 2017 in Venosta, Italy (46 37 0 N, 10 46 0 E) and extracted DNA (YTU-20171001008) was stored at Jiangsu Provincial Key Laboratory of Coastal Wetland Bioresources in Yancheng Teachers University. The National Centre for Biotechnology Information (NCBI) BLAST (http://blast.ncbi. nlm.nih.gov/Blast) and DNAStar packages (DNAStar Inc. Madison, WI) were used to annotate the genome sequence. The MAFFT sequence alignment programme was used to compare genome sequences from T. pityocampa and other species (Katoh et al. 2002). Bayesian inference (BI) and maximum likelihood (ML) analyses were performed using the MrBayes version 3.2.1 and IQ-TREE software, respectively. We selected mtMet þ F þ I þ G4 as the best-fit model for amino acid sequences, as determined by the Modelfinder tool using the Bayesian information criterion (BIC). The mitochondrial genome (mitogenome) is considered a powerful marker for resolving phylogenetic relationships (Galtier et al. 2009). To analyse phylogenetic relationships, we obtained the complete mitogenomes of other species from the GenBank database, and aligned the amino acid sequences of the 13 PCGs using ML and BI methods to reconstruct the phylogenetic tree.
Like those of other lepidopterans, the T. pityocampa mitochondrial genome (GenBank accession no. MH286070) has 37 functional genes and a long-chain non-coding region (AT enrichment region), at a length of 15,737 bp. The overall nucleotide composition is: 37.3% T, 40.5% A, 14.6% C, and 7.6% G, demonstrating an AT bias (A þ T: 77.8%).
From the BI tree of concatenated amino acid sequences from the 13 PCGs, phylogenetic analysis showed that T. pityocampa is very closely related to Ochrogaster lunifer (Figure 1). Thaumetopoea pityocampa was phylogenetically distant from two the outgroup species, Phthonandria atrilineata and Biston panterinaria.

Disclosure statement
No potential conflict of interest was reported by the authors.