A new species of Mollitrichosiphum Suenaga from Taiwan Island (Hemiptera, Aphididae), based on morphological characteristics and DNA sequences

Abstract A new species of Mollitrichosiphum Suenaga, Mollitrichosiphum tumorisiphum Qiao & Jiang, sp. n., from Fagus longipetiolata in Taiwan island is described. Siphunculi of Mollitrichosiphum tumorisiphum in alatae are distinctly swollen on the distal part, unlike those of the other known species in the genus. Updated keys to apterous and alate viviparous females of all known Chinese species of Mollitrichosiphum are provided. The specimens studied are deposited in the National Zoological Museum of China, Institute of Zoology, Chinese Academy of Sciences, Beijing, China and the Natural History Museum, London, United Kingdom.


Introduction
The oriental genus Mollitrichosiphum Suenaga (Greenideinae, Aphididae) is restricted mainly to south-east Asia, and is represented by 11 known species in China (Remaudière and Remaudière 1997, Zhang andQiao 2010). It is distinguishable from other genera of Greenideinae by a series of transverse ridges on the hind tibia. At present, there are six species recorded in Taiwan Island (Tao 1990, 1999, Zhang and Qiao 2010. Amongst aphid samples in the recent survey of Taiwan, two samples of the genus Mollitrichosiphum were found that could not be identified to any known species. Based on morphological features and molecular data, one new species Mollitrichosiphum tumorisiphum Qiao & Jiang, sp. n., feeding on Fagus longipetiolata, from mountainous areas in the northern and central part of Taiwan is described here. This new species differs from any other Mollitrichosiphum species in having alatae with siphunculi distinctly swollen on the distal part. Updated keys to the Chinese species of this genus are provided.

Materials and methods
Morphological description. Aphid terminology and the measurements in this paper generally follow Blackman and Eastop (2006) and Zhang and Qiao (2010). The unit of measurement in this paper is millimetres (mm). Metrical data are listed in Table 1. The holotype and one alate viviparous female of the paratypes (No. 26510) are illustrated in Figures 1-36.
Molecular analyses. Fifty-seven samples belonging to eight Mollitrichosiphum species were included. The standard molecular barcode, mitochondrial cytochrome c oxidase subunit I (COI), and a faster-evolving gene, cytochrome b (Cytb), were used. All sequences were taken from Liu et al. (2013), Zhang et al. (2011) and Zhang et al. (2012). Voucher information and GenBank accession numbers for all samples are listed in Table 2. Multiple alignments were conducted with ClustalX 2.0.12 (Larkin et al. 2007) and then verified manually. Neighbor-joining (NJ) trees and genetic distances were estimated for both COI and Cytb sequences with MEGA 6.06 (Tamura et al. 2013), using Kimura's two-parameter (K2P) model (Kimura 1980). Bootstrap analyses were performed with 1000 replications.
Specimen depositories. The holotype, some paratypes of the new species and the other specimens examined are deposited in the National Zoological Museum of China, Institute of Zoology, Chinese Academy of Sciences, Beijing, China. Two paratypes (including to one apterous and one alate viviparous females) of the new species are deposited in the Natural History Museum (BMNH), London, the United Kingdom. Head. Ocular tubercles dark brown, well developed. Dorsum of head with three pairs of setae between antennae, and 4-6 setae between eyes. Maximum lengths of cephalic setae 4.3-5.7 times as long as basal diameter of antennal segment III. Front flat, antennal tubercles slightly developed (Figs 1, 14). Antennae 6-segmented (Figs 2, 16-17), 0.71-0.72 times as long as body length. Processus terminalis 1.3-1.5 times as long as base of the segment. Antennal segments I-IV, basal half of segment V and of base of segment VI pale brown, other parts of segment V and VI brown. Antennal segments III-VI with short imbrications. Antennal setae pointed. Antennal segment I with only short setae; segments II-V with long and short setae, setae on the inner side of the segment distinctly longer, thicker and more numerous than setae on the outer side of the segment; segments I-VI each with 4-6, 4 or 5 ,16-23, 3 or 4, 3 or 4, (3 or 4)+(4-6) setae, respectively; apex of processus terminalis with 3 or 4 short blunt setae; maximum length of setae on segment III 4.5-5.7 times as long as basal diameter of the segment. Rostrum reaching hind coxae, sometimes abdominal segment I; ultimate rostral segment pale brown, except for brown apex, long and wedge-shaped (Figs 3, 18), 4-6 times as long as its basal width, 1.4-1.8 times as long as second hind tarsal segment; segment IV and V obviously separated; with 3 pairs of primary and 3 pairs of secondary setae.
Mounted specimens. Dorsal setae thick, long and pointed. Head. Head, antennae and ultimate rostral segment dark brown. Dorsum of head with 6 setae between antennae, and 4-6 setae between eyes. Maximum lengths of cephalic setae 4.6-4.9 times as long as basal diameter of antennal segment III. Front flat (Fig. 28). Antennae 6-segmented (Figs 12, 29-30), 0.9 times as long as body length. Processus terminalis 1.4 times as long as base of the segment. Antennal segments III-VI with short imbrications. Antennal setae thick, long and pointed; segments I-VI each with 4, 4 or 5, 18, 4 or 5, 4, 4+5 setae, respectively; apex of processus terminalis with 4 short blunt setae; length of setae on segment III 5.1-5.4 times as long as basal diameter of the segment. Antennal segment III with 7-9 nearly round secondary rhinaria, distributed on basal 2/3 of the segment. Rostrum reaching abdominal segment I; ultimate rostral segment long wedge-shaped (Fig. 31), 5.5 times as long as its basal width, 1.7 times as long as second hind tarsal segment; segment IV and V obviously separated; with 3 pairs of primary and 2-3 pairs of secondary setae.
Thorax. Thorax, femora, tibiae and tasi dark brown. Pronotum with 6 spinal and pleural setae and 3 pairs of marginal setae. Legs slender. Inside of distal half of femora with short spare spinulose imbrications. Hind femur 0.9-1 times as long as antennal segment III. Hind tibia 2 times as long as body, with 69-72 transverse ridges on basal 3/4 of the segment (Fig. 33). Setae on legs short and pointed. Maximum length of setae on hind tibia 2.5-2.9 times as long as mid-width of the segment. Second tarsal segments with transverse imbrications. Chaetotaxy of first tarsomeres: 7, 7, 7. Fore wings with media twice branched and distal 1/3 of CuR 1 Rcurved to media; hind wings with 2 oblique veins.
Abdomen. Abdominal tergites I-VI with spinal, pleural and marginal sclerotic markings fused into a large brown patch; tergites VII and VIII each with one brown transverse patch. Abdominal tergite I with 8-10 setae, tergite VII with 4 setae, tergite VIII with 2 setae. Maximum lengths of marginal setae on abdominal tergite I and dorsal setae on tergite VIII 1.7-2.0 and 3.4-4.0 times as long as basal diameter of antennal segment III, respectively. Venter of abdominal segments III-VI with coarse spinules on pleural and sub-marginal area. Spiracles oval and open, on brown oval spiracular plates. Siphunculi long. tubular, distinctly swollen on distal half (Fig. 34), flange distinct, basal 2/3 of siphunculi dark brown and distal 1/3 brown, with spinules evenly distributed and with spinulose imbrications at apex; 0.5-0.6 times as long as body, 1.8-2 times as long as antennal segment III, 13.9-19.5 times as long as its basal width, 10.4-13 times as long as width of expanded part, 21.3-25 times as long as its distal width; each with 105-120 long and pointed setae. Cauda, anal plate and genital plate brown. Cauda broadly rounded (Fig. 35); 0.26-0.28 times as long as its basal width; with spare spinulose imbrications and 12 setae. Anal plate transversely elliptical, with spare spinulose imbrications and 52-58 setae (Fig. 35). Genital plate transverse oval (Fig. 36) Etymology. The name of this species is derived from its most distinctive feature, its markedly swollen siphunculi. The specific name is composed of "tumor (Latin, =inflated, swelling)" and "siphum (Latin, =tube)".
Diagnosis. The new species is distinctly different from the other known species in the genus, based on siphunculi of alatae distinctly expanded on the apical half. It is similar to the species M. (Me.) niitakaensis (Takahashi), but differs from the latter as follows: body with long and stout dorsal setae, pointed at apex (the latter: at least with some bifurcate dorsal setae); each siphunculus with more than 95 setae (the latter: less than 80); hind tibia with 20-63 short transverse ridges (the latter: with more than 84).
Biology. Colonizing the underside of young leaves of new growth of Fagus longipetiolata. (Figs 38-41).

Molecular analyses
The alignment sequences of COI and Cytb genes included 658 and 666 sites, of which 133 and 129 were parsimony-informative, respectively. The results of NJ analyses of COI and Cytb sequences are summarized. The NJ trees presented here are unrooted and do not reflect phylogenetic relationships, but are used to represent the genetic distance matrices (Foottit et al. 2008). The COI tree (Fig. 42) contained 57 samples of Mollitrichosiphum species and showed eight well-supported clades. All morphologically identified species, including M. tumorisiphum Qiao & Jiang, sp. n., formed monophyletic clusters, indicating that they are genetically distinct from one another. The Cytb tree (Fig. 43) containing 50 samples yielded a similar result, with M. tumorisiphum Qiao & Jiang, sp. n. again retrieved in a distinct clade.
For the sampled known species of Mollitrichosiphum, the mean intraspecific variation was 0.2% (range: 0-0.9%) in COI and 0.1% (range: 0-1.1%) in Cytb. The genetic distance between two distinct samples of M. tumorisiphum Qiao & Jiang, sp. n. was 0 in COI and 0.9% in Cytb. Interspecific genetic divergence between the known Mollitrichosiphum species averaged 8.7% (range: 0.3-12.5%) in COI and 8.1% (range: 0.2-12.3%) in Cytb. Pairwise sequence divergences of COI and Cytb among the Mollitrichosiphum species are presented in Table 3. The mean genetic distance between M. tumorisiphum Qiao & Jiang, sp. n. and the other Mollitrichosiphum species was 10.3% (range: 8.9-11.9%) in COI and 8.8% (range: 7.6%-11.0%) in Cytb, corresponding well to the interspecific divergence between the other known Mollitrichosiphum species.   The results of NJ analyses and genetic distances based on COI and Cytb sequences strongly confirmed that the new morphologically determined species M. tumorisiphum Qiao & Jiang, sp. n. was genetically different from the known Mollitrichosiphum species sampled in this study.