Rediscovery and redescription of two eriophyid mites (Acari, Prostigmata, Eriophyidae) from Baccharis salicifolia (Asteraceae), from Argentina with remarks on the eriophyoid coverflap base

The rediscovery of Aceria cortii Amrine & Stasny and Shevtchenkella baccharis (Keifer) is reported on Baccharis salicifolia (Asteraceae) from Central Argentina and both species are redescribed. Aceria cortii is a gall inducer in leaves and stems of the plant whereas S. baccharis is a leaf vagrant. The topography of the area anterior to the eriophyoid genital coverflap is discussed. This constitutes a first record of S. baccharis for South America.


INTRODUCTION
In the course of investigating leaf galls on Baccharis salicifolia (Ruiz. & Pav.) Pers. (Asteraceae), "chilca", "mulefat", in Cordoba, Argentina, two eriophyid species were collected -one from within leaf and young stem galls, identified as Aceria cortii Amrine & Stasny, 1994, originally described from this plant in the same area, as Aceria baccharidis by Corti in 1917, and one vagrant on the same leaves and identified as Shevtchenkella baccharis (Keifer, 1939), originally described from this same plant, in Cali-fornia, USA. Both species are herein described and illustrated.

MATERIALS AND METHODS
Infested plant leaves and stems were preserved in ethanol 70 % and rapidly conveyed to the laboratory in Brazil. Eriophyid vagrant specimens were needled out of the liquid and gall forming eriophyids from within dissected leaf galls and mounted in modified Berlese medium (Amrine & Manson, 1996) in microcopic preparations for optical microscopy examination and in Hoyer's medium for CLSM.
Measurements are in micrometers and refer to the length of the structure unless otherwise stated. Dimensions from Keifer's descriptions for the same structure are added in brackets. Ventral annuli count start from the first annulus behind genitalia.
CLSM studies were performed at the "Center for Molecular and Cell Technologies" and "Center for Microscopy and Microanalysis" of the Research Park of St. Petersburg State University, Russia.
Male -not seen.
Remarks -One of the females, apparently senile, had a fully grown larva and two eggs inside her body.
Relation to host -This species is a gall inducer on leaves and young stems of B. salicifolia; the galls are glabrous and globose, 1-2 mm in diameter, yellowish, hollow (Fig. 3). Kieffer & Jorgensen (1910, p. 374) referred to "Eriophyidengallen" on Baccharis salicifolia from Mendoza, Argentina. Kieffer & Herbst (1911, p. 703) refer to the galls mentioned in the previous paper , however inform that they were collected from Baccharis subulata D. Don ex Hook. & Arn. (= Baccharis juncea (Cass.) Desf.), and which they attribute to Eriophyes baccharidis n.sp., but, they only described the gall. Amrine & Stasny (1994) made a new combination, transferring the mite species to Aceria baccharidis and updated the host plant name to Baccharis juncea. At this point we do not have sufficient information to further comment on Aceria baccharidis: there is no description nor figure of the mite, no material (gall or mite) from B. juncea exists and Amrine & Stasny (1994) maintained this species distinct from A. cortii. Specimens from Baccharis juncea in Mendoza, Argentina need to be found and   carefully described. If conspecific with Aceria cortii, then Aceria baccharidis (Kieffer & Herbst, 1911) becomes the senior synonym.
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 and1951), in the drawings of O. glabratae and O. juglandis, respectively, this coverflap base appears as a single strcuture and in Keifer (1960Keifer ( , 1961Keifer ( 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.