Rubiaphis, Stekolshchikov & Novgorodova, 2020

Stekolshchikov, Andrey V. & Novgorodova, Tatiana A., 2020, Rubiaphis, a new aphid genus from the Altai Republic (Homoptera: Aphididae, Macrosiphini), Zootaxa 4718 (1), pp. 145-150 : 145-146

Rubiaphis gen. nov.

Type species. Rubiaphis altaicus sp. nov.

Description. Apterous viviparous female. Body elongate-elliptical. Body and appendages are not sclerotized, semitransparent. Surface of head and abdominal tergite VI with poorly noticeable reticulation (margins of cells formed by thin, irregular lines), of dorsal and ventral sides of thorax and abdominal tergites I–V smooth or slightly wrinkled, on tergite VII with long rows of flat or pointed spinules, which on tergite VIII are partially fused to form long scales; ventral surface of abdomen with long rows of small pointed spinules sometimes forming strongly stretched reticulate cells. Setae on head and dorsal surface of body very long, pointed or capitate, on ventral surface of body finely pointed, on legs pointed, on antennae short and blunt. Marginal tubercles are present only on the prothorax, they are small, narrowly conical or papilliform. Spinal tubercles absent. Frons with clearly marked frontal tubercles, median tubercle large, strongly protuberant, almost rectangular (with slightly rounded edges); median tubercle with two long setae and projecting beyond antennal tubercles, or (rarely) not reaching the level of antennal tubercles. Antennae 5-segmented, without secondary rhinaria. Compound eyes are well-developed but consist of relatively few ommatidia and with triommatidia on relatively small and sometimes almost invisible ocular tubercles. Ultimate rostral segment elongated wedge-shaped with straight sides. Arms of mesosternal furca separated. Legs normal. Chaetotaxy of first tarsal segments 3, 2, 2 or 3, 3, 2, but often one fore tarsus with 2 setae or one middle tarsus with 2 setae, and the other with 3 setae. Spiracles reniform, peritremes on abdominal sternites I and II widely spaced, the distance between the centres of spiracles on abdominal segments II and III 1.04–1.37 (1.23) as long as the distance between the centres of spiracles on segments I and II. Siphunculi relatively long, slightly conical, with relatively wide base, distinctly tapering towards the upper third, then widened to the apex, sometimes slightly Sshaped and curved outward in the apex, imbricated, covered by large scales, without any trace of polygonal reticulation. Subgenital plate oval. Cauda elongated triangular with widely rounded apex.

Etymology. The generic name Rubiaphis is of feminine gender and derived from the Latin word “ rubus ” (= bramble, blackberry bush) in the genitive case (“ rubi ”) and the new Latin word “ aphis ” (= plant-louse).

Diagnosis. An important feature of the new genus is that the distance between the centres of the spiracles on abdominal segments II and III is much less than twice the distance between the centres of the spiracles on segments I and II, a feature typical for genera belonging to the tribe Aphidini . In fact, this is one character that has hitherto reliably discriminated between the two tribes of the subfamily Aphidinae . However, a combination of other characters, such as the complete absence of marginal tubercles on the abdomen including the absence of tubercles on I and VII segments, the shape of the frons, the structure of the cuticle, and the shape of the siphunculi and the cauda, indicates that the new genus belongs to the tribe Macrosiphini . Rubiaphis is related to Myzaphis van der Goot, 1913 , Chaetosiphon Mordvilko, 1914 , Longicaudus van der Goot, 1913 and Richardsaphis Kanturski et Barjadze ex Kanturski, Barjadze, Jensen et Wieczorek, 2018 , which have been regarded as so called “Myzaphidines” ( Richards 1963; David et al. 1970; Kanturski et al. 2018). The similarity between the new genus and the other “Myzaphidines” is not only morphological, but also biological—their host plants belong to the family Rosaceae . Of these four genera, Rubiaphis is closest to Myzaphis from which, however, apterous viviparae are easily distinguishable by the following features: surface of thorax and abdominal tergites I–V smooth (dorsal cuticle of Myzaphis rugose or wrinkled); setae on head and dorsal surface of body very long, pointed or capitate (head and abdominal setae of Myzaphis very short with variously shaped apices); antennae 5-segmented (antennae of Myzaphis 6-segmented) with relatively long (162–225 µm) processus terminalis (processus terminalis of Myzaphis relatively short— 50–150 µm; Kanturski et al. 2018); antennae 0.75–1.06 of body (antennae of Myzaphis only about half of body); ultimate rostral segment relatively long, elongated wedge-shaped (ultimate rostral segment of Myzaphis relatively short, only wedge-shaped); first tarsal segments with 3, 2, 2 or 3, 3, 2 setae (all first tarsal segments of Myzaphis with 5 setae); spiracular apertures reniform, not covered by opercula (spiracular apertures of Myzaphis partly covered by opercula). It should be noted, however, that the presence of 5-segmented antennae in specimens of the new genus may be due to the fusion of the 3rd and 4th segments, caused by a lack of nutrition, which is often found in individuals of various species of aphids in mid-summer, so this character cannot be considered as an absolute.

Apterous viviparae of Rubiaphis are easily distinguishable from those of Richardsaphis by the following features: surface of thorax and abdomen smooth (dorsum of Richardsaphis sclerotic and wrinkled); antennae 5-segmented (antennae of Richardsaphis 6-segmented) with relatively long (162–225 µm) processus terminalis (processus terminalis of Richardsaphis short— 50–60 µm ( Kanturski et al. 2018)); ultimate rostral segment relatively long, elongated wedge-shaped (ultimate rostral segment of Richardsaphis is relatively short, oblong triangular with blunt apices); first tarsal segments with 3, 2, 2 or 3, 3, 2 setae (all first tarsal segments of Richardsaphis with 2 setae).

Species of the genus Chaetosiphon are characterized by the presence of 5 hairs on all first tarsal segments and conspicuous capitate setae on dorsum of apterae, whereas specimens of the new genus have 3, 2, 2 or 3, 3, 2 setae on first tarsal segments and blunt or very weakly capitate setae on dorsum. Species of the genus Longicaudus have short siphunculi, a long cauda and a very long 3rd antennal segment, whereas siphunculi of apterae of Rubiaphis are 2.86–3.27 times as long as cauda and the 3rd antennal segment is of normal length.