Shevtchenkella baccharis (Keifer, 1939)

Flechtmann, C. H. W., Arana, M., Ciarrocchi, F., Chetverikov, P. E. & Amrine Jr., J. W., 2015, Rediscovery and redescription of two eriophyid mites (Acari, Prostigmata, Eriophyidae) from Baccharis salicifolia (Asteraceae), from Argentina with remarks on the eriophyoid coverflap base, Acarologia 55 (4), pp. 387-396 : 393-395

Shevtchenkella baccharis (Keifer, 1939)

( Fig. 4 , 5 )

Oxypleurites baccharis Keifer, 1939: 238 . Tegonotus baccharis, Newkirk & Keifer, 1971: 7 . Shevtchenkella baccharis, Amrine & Stasny, 1994: 283 .

Female (n = 6). Body fusiform, 158 – 180 [135 – 150], widest at level of shield, 67 – 73 [60].

Gnathosoma : projecting down, dorsal pedipalp genual seta (d) 5 – 7, pedipalp coxal seta (ep) 2 – 3, chelicera stylets 15 – 19.

Prodorsal shield: 60 – 66 [46], 70 – 73 [60] wide, shield design very indistinct under light microscopy, with two longitudinal shallow grooves on anterior shield half and which merge posteriorly, and one pair of longitudinal shallow grooves on middle third of shield. Shield surface rough, irregular. Frontal lobe as figured, 7 – 11, base 16 – 20 wide. Scapular seta (sc) 5 – 6 [4.5], near shield rear margin, 33 – 35 [28] apart, directed backwards.

Legs: leg I: 28 – 31 [29]; femur 8 – 11, basiventral femoral seta (bv) 8 – 11; genu 5 – 6, antaxial genual seta (l") 18 – 26 [22]; tibia 8 – 10 [6.75], paraxial tibial seta (l’) basal, 3 – 4; tarsus 5 – 7 [6.5], dorsal tarsal ou paraxial fastigial seta (ft’) 6 – 19, lateral tarsal or antaxial fastigial seta (ft") 9 – 25, paraxial unguinal seta (u’) 3 – 5, tarsal solenidion (ω) 4 – 5 [6.5], slightly knobbed, empodium 4 – 5, four-rayed, apical ray Yshaped. Leg II 28 – 33 [28]; femur 9 – 10, bv 9 – 11; genu 5 – 6, l" 3 – 5 [4.5]; tibia 6 – 8 [6.5]; tarsus 5 – 6 [6.5], ft’ 4 – 5, ft" 18 – 19, u’ 4 – 5, solenidion 5 – 6 [6], empodium 4 – 5, four-rayed.

Coxisternal area: coxae I approximate, fused at level of seta 1a, prosternal apodeme (sternal line) 5 – 7. Coxae apparently smooth under light microscopy. Coxa I: anterolateral seta on coxisternum I (1b) 7 – 11, 12 – 15 apart; proximal seta on coxisternum I (1a) 19 – 23, 8 – 10 apart; proximal seta on coxisternum II (2a) 27 – 40 [26], 19 – 25 apart. Coxigenital area with 4-6 annuli [5], microtuberculate, microtubercles about half the length of annulus.

Basal coverflap rectangular shaped, apparently smooth.

Genitalia 22 – 24 [24] wide, 13 – 16 [15] long, coverflap with 12 – 14 [10 – 12] ridges; proximal seta of coxisternum III (3a), on lateral margin of genitalia, 14 – 17 [13].

Opisthosoma with a central longitudinal ridge. Total dorsal annuli 17 – 19 [18 – 19], with narrow, numerous microtubercles; total ventral annuli from genitalia rear margin 54 – 63 [50, corrected in ES VII], microtuberculate. Lateral seta (c2) 25 – 35 [31], on first or second annulus behind genitalia rear margin; first ventral seta (d) long, surpassing basis of second pair, 40 – 48 [48], 26 – 30 apart, on annulus 14; second ventral seta (e) 10 – 11 [17], 14 – 18 apart, on annulus 29 – 33; third ventral seta (f) 22 – 25 [24], 19 – 21 apart, on anulus 49 – 58 or 4 th- 5 th from rear. Caudal seta (h2) 40 – 51 [40], accessory seta (h1) 3 – 4.

Male (n = 3) Smaller than female, 145 – 157, 41 – 55 wide. Prodorsal shield 54 – 55, 59 – 64 wide. Seta sc 4, 27 – 32 apart. Frontal lobe 7 – 9, basis 21 – 22 wide.

Legs: leg I 27 – 28; femur 6 – 9, bv 7 – 10; genu 4 – 5, l" 16 – 26, tibia 6 – 7, l’ 3; tarsus 5 – 6, ft’ 11 – 17, ft" 16 – 18, u’ 3 – 4, solenidion 5 – 6, empodium 4 – 5, four-rayed. Leg II 26 – 28; femur 9, bv 7 – 10; genu 3 – 5, l" 3; tibia 4 – 5; tarsus 5 – 6, ft’ 2 – 3, ft" 15 – 17, u’ 2, solenidion 5 – 6, empodium 4, four-rayed.

Coxisternal area: 1b 5 – 8, 11 – 13 apart; 1a 18 – 20, 8 – 10 apart; 2a 23 – 31, 23 – 25 apart. Prosternal apodeme 6 – 7; coxigenital annuli 6.

Genitalia 16 – 17 wide, 7 – 9 long; 3a 10 – 13.

Opisthosoma: c2 20 – 23, on annulus 1; d 38 – 49, 25 – 28 apart, on annulus 9; e 7 – 11, 12 – 15 apart, on annulus 23; f 19 – 22, 18 – 22 apart, on annulus 45 or 5 th from rear. Total dorsal annuli 17 – 18, total ventral annuli 51. Setae h2 31 – 44, h1 2 – 3.

Materiel examined — 17 females, 7 males, vagrant on leaves of Baccharis salicifolia (Ruiz. & Pav.) Pers. (Asteracee), Cordoba, Argentina , collected by MA and FC, October 2014, on 13 microscopic preparations, deposited in the Mite Reference Collection of Departamento de Entomologia e Acarologia , Escola Superior de Agricultura " Luiz de Queiroz !, Universidade de Sªo Paulo , Piracicaba, Sªo Paulo, Brazil .

Remarks — The geographical distribution of the host plant, Baccharis salicifolia, ranges from Southwestern USA to Argentina. Keifer (1939a) described the female of Oxypleurites baccharis (now placed in Shevtchenkella ) from this plant from Riverside, California, USA. A recent collection from the same plant in Argentina revealed a Shevtchenkella in conformity with Keifer’s species and which is here considered conspecific with it, although we have not seen the type specimens, deposited in the Keifer Collection, USDA, Beltsville, Maryland, USA, which deteriorated and turned black (R. Ochoa personal information).

The finding of S. baccharis in Central Argentina constitutes the first record of this species from South America. Following Ballari et al. (2013), S. baccharis is the eighth species of the genus described from South America and the second from Argentina. In this country, the other species is S. marceloi Flechtmann, described from leaves of Tessaria dodonaefolia (Hook & Arn.) Cabrera, also an Asteraceae .

Later, Keifer (1939b) described Oxypleurites acidotus, a vagrant species close to O. baccharis , from Baccharis pilularis DC, from San Francisco, California, USA. He stated that acidotus differs from baccharis by the "lack of striae on the dorsal ridge, the large knob" on the tarsal solenidion, and in "the increase in tergites and sternites in acidotus over baccharis ": 22 dorsal and 60-65 ventral anuli in acidotus while respectively 17 and 50 in baccharis .

Remarks on the topography of the area anterior to eriophyoid genital coverflap

In the descriptions/illustrations of a few eriophyid species the genital coverflap base may sometimes be illustrated as paired platelike structures, partially fused medially, or consolidated into a single piece, usually ornamented similarly to leg coxae or to the coxigenital annuli. However, the coverflap base is not usually referred to in the descriptions except in a very few instances. In Keifer (1938) this structure is illustrated, apparently for the first time, in the drawing of Platyphytoptus sabinianae, as one single piece, however, it is medially indented;in Keifer (1938), in the illustration of Stenacis convolvens (Nalepa), it is drawn as a solid rectangular structure with the same ornamentation as the leg coxae; in Keifer (1939a) this structure is outlined as a rectangle in the drawing of Oxypleurites baccharis ; in Keifer (1940 and 1951), in the drawings of O. glabratae and O. juglandis, respectively, this coverflap base appears as a single strcuture and in Keifer (1960, 1961 and 1979), in the drawings of Ditrymacus athiasella, O. solidaginis and Eriophyes spermaphaga, respectively, again it appears as a single structure. In Navia & Flechtmann (2003), in the drawings of Notostrix miniseta, the coverflap base appears to have paired fields, deeply indented medially and was considered as the basal part of the "epigynum" or coverflap and in Navia et al. (2011), in the drawing of Abacarus doctus, the coverflap base is paired and the authors referred to the composite of the "epigynum" (coverflap) plus these two structures as a "genital coverflap resembling a curtain".

With the introduction of Confocal Laser Scanning Microscopy in the study of eriophyoid mites, Chetverikov et al. (2014) in Pentasetacus araucariae show the presence of a short median ridge dividing the coverflap base into two parts and which they called the pregenital plate. In the PCLM microphotographs of Phyllocoptes sp. in Chetverikov (2014a, fig. 2B) the paired pregenital plates (coverflap base) are evident and the image displays an ornamentation pattern similar to that of leg coxae. Chetverikov et al., (2015), in the rediagnosis of the genus Neoprothrix , also identified a pair of subcuticular "indistinct lateral plates separated medially by a short cuticular ridge", which may be a unique adaptation in this species due to the great distance between the coxae and the genitalia. Finally, Chetverikov (2014b, p. 153, footnote 7 and fig. 9C) reported that Oziella spp. have two prominences anterior to the basal part of the genital coverflap, which may be considered to be homologous to the basal coverflap in other species above. The remarkable resemblance of the ornamentation of the pregenital plate to that of coxae in many eriophyoids, and the fact that this plate can be divided into two parts might indicate that this plate is a remnant (rudiment) of the coxae of the legs III or IV. Searching for new examples and careful description of pregenital area in new species will help to clarify this putative homology.

Figures

FIGURE 4: Shevtchenkella baccharis Keifer – AV anterior ventral aspect of female. D dorsum of female. E empodium. GM male genitalia. IGF internal genital structures of female. L1 leg I. L2 leg II.

FIGURE 5: CLSM images of female of Shevtchenkella baccharis (A,B – autofluorescence; C – transmitted light). A – dorsal view, B – ventral view, C – coxigenital area. Scalebar: A, B=70 µm, C=10 µm.