Metopolophium arcticum, Stekolshchikov & Khruleva, 2020

Stekolshchikov, Andrey V. & Khruleva, Olga A., 2020, Contribution to the aphid fauna (Homoptera, Aphidinea) of the Taymyrsky Dolgano-Nenetsky District and the krai city of Norilsk, with descriptions of two new species of the genus Metopolophium, Zootaxa 4748 (1), pp. 87-118 : 96-101

Metopolophium arcticum sp. nov.

( Figs. 2–15 , Table 1 )

Type material. Holotype: fundatrix, No. 10891, slide No. 32, specimen No. 1 (left specimen in the lower row), “ Metopolophium arcticum sp. nov., 2.vii–4.viii.2004, Krasnoyarsk Krai, Taymyrsky Dolgano-Nenets District, near to Medusa Bay, Varavikova River (13 km south of Dikson Vill. , 73° 24ˊ N, 80° 44ˊ E), gravelly south-facing slope of the river terrace with spotted willow-dryad-moss cover, pitfall traps, leg. D.V. Osipov ” . Paratypes: 11 fund., No. 10889, the same locality and biotope as holotype, 22–27.vii.2002, pitfall traps; 17 fund., 17 males, 10 ovip., No. 10891, the same locality and biotope as holotype, 2.vii–4.viii.2004, pitfall traps; 3 fund., 1 ovip., No. 10895, Krasnoyarsk Krai, Taymyrsky Dolgano-Nenets District, near to Efremov Kamen` Bay , Maksimovka River (32 km south of Dikson Vill. , 73° 14ˊ N, 80° 44ˊ E), gravelly dry plot in the river valley with a forb-moss-dryad cover, 5–30.vii.2004, pitfall traps .

Holotype is deposited at ZIN RAS; paratypes are deposited at ZIN RAS, the Natural History Museum ( London , United Kingdom) and Muséum national d’Histoire naturelle (Paris, France).

Etymology. Latin neutral adjective arcticum (northern, arctic, from the Arctic), pertaining to the Arctic.

Description. Fundatrix. Body broadly elliptical, 1.7–2.0 (1.8) times as long as wide. Colour of living specimens unknown. Cleared specimens with antennae gradually darkening to the apex from very light-brown 1st segment to brown processus terminalis; brown ultimate rostral segment, apices of tibiae and tarsi; legs and siphunculi lightbrown; head, rostrum (except ultimate rostral segment), peritremes, anal and subgenital plates and cauda very lightbrown. Thorax and abdomen not sclerotized, pale, membranous; only VIII abdominal tergite with very light-brown and almost invisible band. Surface of head, dorsal side of thorax and abdominal tergites I–VI wrinkled; sometimes on thorax and abdominal tergites I–IV intensely wrinkled, on VII abdominal tergite with short rows of small pointed spinules, which on VIII abdominal tergite partially fuse to form scales; ventral side of thorax smooth with long rows of small pointed spinules in base of coxae; ventral side of abdomen with long rows of small spinules, sometimes forming strongly stretched cells. Setae on dorsal surface of thorax and abdomen strongly blunt, almost rod-like, or weakly capitate; setae on ventral surface of thorax and abdomen pointed or rarely blunt. Paired or unpaired mar- ginal tubercles were often present on pro-, meso-, and metathorax and on abdominal segments II–V; total number of marginal tubercles on whole body 0–13 (2.3–6.4). Marginal tubercles not large (medial diameter of siphunculus 1.3–5.7 (2.1–3.4) times as long as width of the largest marginal tubercle), from semicircular to flat. Spinal tubercles absent. Head with epicranial suture more or less distinct. Frontal tubercles well developed, antennal tubercles rather high, divergent, median tubercle not high, but clearly marked; frons with sinus, ratio of depth of sinus to distance between bases of antennae 0.07–0.19 (0.14). Setae on head blunt or weakly capitate. Antennae 6-segmented, 1st and 2nd antennal segments lightly wrinkled, almost smooth, 3rd–6th segments with large scales, almost invisible on 3rd but well-defined on 5–6th segments. Third antennal segment rarely with rhinaria; total number of rhinaria on segment 0–2 (0.0–0.7), situated near base of segment, round or oval, small (with internal diameter 8–13 μm). Antennae with blunt or weakly capitate setae on 1st–4th segments and pointed ones on 5th–6th. Rostrum reaching mesothorax. Ultimate rostral segment elongate, wedge-shaped, with slightly but clearly convex sides, 1.5–1.8 (1.7) times as long as its basal width. Legs long, setae on legs blunt or pointed, on tarsi only pointed. Chaetotaxy of first tarsal segments 3, 3, 3. Arms of mesosternal furca connected by wide base. Spiracles reniform. Peritremes on abdominal segments I and II widely spaced. Siphunculi with distinct and relatively large flange, with imbrication increasing distally, almost cylindrical but with conical base. Subgenital plate oval, with pointed setae on anterior half and blunt or pointed setae along the hind margin. Setae on anal plate finely pointed. Cauda sword-shaped or, rarely, fingershaped, with pointed apex and a constriction at basal third, and long, finely pointed setae.

Measurements of holotype. Body—1903×1091; antenna—1055: III—245×24 (in the middle), IV—126, V— 185, VI—132+210; hind femur—472; hind tibia—832; siphunculus—326×41 (in the middle); cauda—243×152 (at base) ×114 (before base). For more biometric data see Table 1 .

Male. Apterous. Body elongate elliptical, almost spindle-shaped, 2.0–2.5 (2.2) times as long as wide. Colour of living specimens unknown. Cleared specimens with brown head; 3rd–6th antennal segments (except base of 3rd segment), ultimate rostral segment, apices of tibiae and tarsi, with 1st–2nd antennal segments, legs and siphunculi light-brown; base of 3rd antennal segment, rostrum (except ultimate rostral segment), peritremes, anal and subgenital plates and cauda very light-brown. Thorax not sclerotized, pale, membranous; abdominal dorsum with brown or light-brown spinal and large marginal sclerites (often hardly visible) on tergites I–VI, brown or light-brown intersegmental muscle sclerites on tergites II–VI and light-brown bands on tergites VII–VIII; spinal and marginal sclerites on tergites I–VI sometimes fused and forming band or, rarely, strongly interrupted single shield. Surface of abdominal tergite V with sporadic small pointed spinules, which on VI tergite unite in short rows. Paired or unpaired marginal tubercles occasionally present on prothorax and on abdominal segments I–V; total number of marginal tubercles on whole body 0–7 (2.2). Head without or rarely with epicranial suture. Frontal tubercles well developed, antennal tubercles rather high, divergent, median almost invisible, practically absent; ratio of depth of sinus to distance between bases of antennae 0.04–0.19 (0.11). Antennae 6-segmented or, rarely, almost or 5-segmented as a result of partial or complete fusing of 3rd and 4th segments. Second antennal segments with short scales on ventral side. Third antennal segment with 22–38 (32.3), 4th segment with 17–27 (21.8), 5th antennal segment with 10–21 (15.1) secondary rhinaria and base of 6th antennal segment with 0–1 (0.1) secondary rhinaria. Rostrum reaching metathorax. Ultimate rostral segment 1.7–2.1 (1.9) times as long as its basal width. Peritremes on abdominal segments I and II separated by a distance lesser than diameter of peritreme, sometimes continuous. Cauda elongate triangular or sword-shaped, with almost pointed apex and a weak constriction at basal third.

Oviparous female. Body broadly elliptical, 1.7–2.0 (1.8) times as long as wide. Colour of living specimens unknown. Marginal tubercles on abdominal segment V absent; total number of marginal tubercles on whole body 0–7 (3.3). Head with or without epicranial suture. Ratio of depth of sinus to distance between bases of antennae 0.12–0.24 (0.18). Third antennal segment without rhinaria. Peritremes on abdominal segments I and II continuous. Cauda short, finger-shaped. Hind tibiae weakly swollen in basal half, with 35–82 (53.0) round or oval small pheromone plates located in basal two thirds of tibia.

Distribution. Known only from Krasnoyarsk Krai, Taymyrsky Dolgano-Nenets District (north-western Taymyr).

Biology. Life cycle unknown, probably monoecious, holocyclic. In all three samples of this species, apterous viviparous females (except fundatrices) were absent, including in pitfall traps, where material accumulated from early July to early August. This may be an accident, but most likely it is associated with a greatly shortened life cycle where the fundatrix can directly produce males and oviparae.A similar life cycle is known in some other High Arctic species of aphids ( Strathdee et al. 1993; Gillespie et al. 2007). In any case, the cycle of the new species is short and, most likely, monoecious, since a relatively short period of time that passes from the fundatrices to the appearance of the amphigonic generation is not enough for migration to the secondary host and subsequent remigration.

The area of discovery of the new species is well studied (arthropods were harvested using pitfall traps for 6 seasons in many biotopes). However, the new species was collected only in two biotopes, similar in vegetation, and located at a distance of about 20 km from each other. These are dry gravel banks of the river with a grass-dryad-moss cover, where the snow melts early. At one site (Varavikova River), the species was collected during two seasons (2002 and 2004). For species of the genus Metopolophium , the typical hosts are grasses ( Poaceae ), either as secondary host of dioecious species or as the only host of monoecious ones. In north-western Taymyr, there are about 25 grass species of which about 10 are quite common ( Matveyeva & Zanokha 1997). However, M. arcticum was found in biotopes where Dryas punctata Juz. (Rosaceae) forms the principal vegetation cover (the name of the species prevailing in such communities is given by Matveyeva 1998), and grasses are present in small numbers. Thus, although it cannot be ruled out that the new species lives on one of the grasses that are present, it is more likely that it has moved to a monoecious existence on a dryad. This can be facilitated by the fact that this plant belongs to the Rosaceae family, on whose plants ( Rosa ) dioecious Metopolophium species develop.

Systematic relationships. The aphid genera Metopolophium and Acyrthosiphon are similar, differing in only one significant morphological feature: in Metopolophium , the median frontal tubercle is usually well developed, whereas it is usually absent or not easily visible in Acyrthosiphon . Unfortunately, the degree of its manifestation varies within each genus and it is sometimes difficult to draw a line between extreme variants of each genus. Individuals of the M. arcticum have a well-developed median frontal tubercle ( Fig. 3 ) that allows us to place it confidently in Metopolophium . Additional characters that can be attributed to Metopolophium are the almost complete absence of rhinaria on the third antennal segment (species of the genus Acyrthosiphon usually have many) and a relatively small number of additional setae on the ultimate segment of the rostrum (species of Acyrthosiphon can have up to 23). Species of the Sitobion subgenus Metobion are also similar to M. arcticum , but all species of this subgenus differ in having a short rostrum, reaching just past fore coxae, and a short ultimate rostral segment that is blunt, about as long as broad, less than 0.7 times as long as the second segment of the hind tarsus, and bearing 4 or fewer accessory setae. In addition, the siphunculi of most Metobion species have subapical reticulations (up to 4 rows) although sometimes these rows of polygonal cells are weakly developed, consisting of several isolated large scales. Metopolophium arcticum never has subapical reticulations on its siphunculi.

There are 21 currently known species of the genus Metopolophium ( Favret 2019) . Morphs other than the apterous and alate viviparous females are known for 13 of them. The new species differs from almost all the others by low values of the ratio of the length of the processus terminalis and the length of base of the last antennal segment (PT/BASE) and, conversely, the high ratio of the length of ultimate rostral segment and the length of the 2nd segment of the hind tarsus (URS/HT2), as well as by other characters ( Table 2 ).

In the genus Metopolophium , as in many species of the subtribe Macrosiphina , the oviparous females have a high degree of similarity with the apterous viviparous females of the summer generations. This allows, with a high degree of reliability, a comparison between oviparous females of the new species and apterous viviparous females of the summer generations of those species for which the ovipara is unknown: M. berberinutritum Zhang, Chen, Zhong et Li, 1999 , M. caudatum ( Pergande, 1900) , M. darjeelingense Ghosh, 1970 , M. darjilingense Raychaudhuri, Ghosh et Basu (1975) 1978 , M. longicaudatum ( David et Hameed, 1975) , M. mukhamadievi Akhmedov, 1988 , M. palmerae ( Hille Ris Lambers, 1949) and M. rosaescutum Zhang in Zhang et al., 1992 . The new species differs from most of the listed species by the same two ratios (PT/BASE and URS/HT2) ( Tables 1 and 2 ). Only in M. darjilingense is URS/HT2 high, even higher than in the new species, but PT/BASE is also high. The values of PT/BASE and URS/HT2 are unknown for M. caudatum , but in this species the ratio of the length of siphunculi to the length of cauda is less 1.0, whereas in M. arcticum it is much greater: 1.31–1.86. Metopolophium arcticum differs from a number of species— M. albidum Hille Ris Lambers, 1947 , M. alpinum Hille Ris Lambers, 1966 , M. chandrani ( David et Narayanan, 1968) , M. dirhodum (Walker, 1849) , M. fasciatum Stroyan, 1982 , M. festucae ( Theobald, 1917) , M. lacheni Agarwala, Mondal et Raychaudhuri, 1982 , M. montanum Hille Ris Lambers, 1966 and M. tenerum Hille Ris Lambers, 1947 —by the presence of apterous males, whereas only alate males are known in the other species.

In connection with the insufficiently precise separation of Metopolophium and Acyrthosiphon , the described species should be compared with those Acyrthosiphon species found in the northern territories— Acyrthosiphon assiniboinensis Robinson, 1973 , A. auctum (Walker, 1849) , A. boreale Hille Ris Lambers, 1952 , A. brachysiphon Hille Ris Lambers, 1952 , A. brevicorne Hille Ris Lambers, 1960 , A. churchillense Robinson, 1979 , A. ignotum Mordvilko, 1914 , A. knechteli ( Börner, 1950) , A. loti ( Theobald, 1913) , A. malvae ( Mosley, 1841) , A. pisum ( Harris, 1776) , A. svalbardicum Heikenheimo, 1968 . Only in the apterous viviparous female of three of these species— A. auctum , A. brevicorne and A. svalbardicum —the values of PT/BASE are lower than 2.8. At the same time, PT/BASE for the oviparous female of A. svalbardicum is 1.06–1.56 (1.56–2.35 for M. arcticum ), ratios of length of siphunculus and length of body, and length of siphunculus and length of cauda for apterous viviparous female of A. auctum is 0.11–0.17 and 0.85–1.33 respectively (0.16–0.21 and 1.31–1.86 for oviparous female of M. arcticum ), A. brevicorne has very short dorsal setae on abdominal tergite III (about 0.25 times as long as articular diameter of 3rd antennal segment) (0.84–1.56 for oviparous female of M. arcticum ) and the values of PT/BASE for oviparous female of A. brevicorne is 2.30–2.80 (1.56–2.35 for oviparous female of M. arcticum ).

Figures

FIGURES 2–15. Metopolophium arcticum sp. nov., fundatrix, oviparous females and males. 2, body of fund.; 3, frons of fund.; 4, antenna of fund.; 5, antenna of ovip.; 6, antenna of male; 7, ultimate rostral segments of fund.; 8, hind tarsus of fund.; 9, hind tibia of ovip.; 10, siphunculus of fund.; 11, siphunculus of male; 12, siphunculus of ovip.; 13, cauda of fund.; 14, cauda of male; 15, cauda of ovip.