A new oak-feeding species of Lachnus Burmeister and some remarks on the taxonomic status of L. chosoni Szelegiewicz (Hemiptera, Aphididae, Lachninae)

A new species, Lachnus pseudonudus Kanturski & Wieczorek, sp. n., associated with Quercus ithaburensis subsp. macrolepis is described and figured in detail from specimens collected in Turkey. The lectotype and paralectotypes of L. crassicornis, a species associated with Quercus ithaburensis subsp. ithaburensis, are designated. The taxonomic position of L. chosoni, a poorly known species from Korea previously treated as a synonym of L. pallipes, is discussed. Morphological and biometric characters of the studied species are given. An identification key to species belonging to the “pallipes” group is provided.


Introduction
The genus Lachnus Burmeister, 1835 comprises about 20 species associated with deciduous trees from the genera Castanea, Castanopsis, Fagus, Quercus (Fagaceae), Hippophae (Eleagnaceae), Salix (Salicaceae), Ficus (Moraceae) and Casuarina (Casuarinaceae) and living on the bark of tree trunks, branches or main roots (Heie 1995;Binazzi and Remaudière 2010).Aphids from this genus are characterised by medium to large body size, long hind legs and pigmented wings in alatae.Key morphological features of Lachnus include also the terminal process of the antenna with 2-7 subapical setae, and primary rhinaria with a sclerotic rosette.The apical segment of the rostrum is short and with a button-shaped apical part (Szelegiewicz 1978;Blackman and Eastop 1994).Among representatives of the genus Lachnus, most species are Fagaceae-feeders, associated mostly with oaks (Quercus spp.).According to Binazzi and Remaudière (2010), this group of species living on the Fagaceae can be divided into subgroups with or without distinct mesosternal tubercles in apterous viviparous females.The group lacking these tubercles comprises L. crassicornis Hille Ris Lambers, 1948, L. longirostris (Mordvilko, 1901) and L. pallipes (Hartig, 1841) (the "pallipes" group) and is characterised also by very long setae on the apical part of the hind tibiae in addition to the normal ones.Among the above mentioned species the status of L. longirostris is questionable; i.e. this species is treated as a synonym of L. pallipes (Szelegiewicz 1975;Blackman and Eastop 1994), which has been confirmed by recent molecular studies (Mróz et al. 2013).Moreover, the species L. chosoni Szelegiewicz, 1975 seems to be closely related to this group, also treated by some authors as a synonym of L. pallipes (Blackman andEastop 1994, 2014;Remaudière and Remaudière 1997).In addition, Blackman andEastop (1994, 2014) suggested that in the collection of the Natural History Museum, London, UK (BMNH) specimens determined as L. crassicornis but most probably belonging to an undescribed species related to the "pallipes" group are present.
The aim of this paper is to define the taxonomic status of the species belonging to the "pallipes" group.On the basis of the material deposited in the BMNH a new, hitherto unknown species is described.The lectotype and paralectotypes of L. crassicornis are designated.Based on a reinvestigation of the type material of L. chosoni deposited in the Zoological Institute, Polish Academy of Sciences, Warsaw, Poland (ZMPA) the status of this species is discussed.An identification key to species belonging to the "pallipes" group is provided.The specimens were examined using the light microscope Nikon Ni-U.Drawings were made with a camera lucida.Measurements are given in mm (Table 1 and 2).Measurements and ratios of the first segment of hind tarsus (HT I) were made according to Szelegiewicz (1978) and Heie (1995).

Lachnus pseudonudus
Diagnosis.The new species can be distinguished from L. crassicornis as well as from the other Lachnus species by the sparse dorsal chaetotaxy and extremely short, inconspicuous setae with blunt, slightly spatulate, capitate or club-shaped apices.The new species is also characterised by siphunculi with a very well-developed and almost transparent flange with 8-10 rows of polygonal reticulation.Main morphological and biometric differences between L. pseudonudus Kanturski & Wieczorek, sp.n. and L. crassicornis are given in Table 2.
Etymology.The name of the new species is derived from characteristically short and inconspicuous setae on the dorsal part of the thorax and the abdomen.

Discussion
The Fagaceae-feeding species of the genus Lachnus form morphologically related groups (Binazzi and Remaudière 2010).The "pallipes" group is characterised by the lack of mesosternal tubercles and two types of setae on the hind tibiae: setae as long as or slightly longer than the diameter of the middle part of the tibiae, and some which are distinctly longer.In this group of species L. pallipes is characterised by the longest tibial setae situated not only on the posterior part of the tibiae but usually also distributed individually along almost the whole length of the tibiae.In that species, the body is also covered with numerous setae, but contrary to L. crassicornis and L. pseudonudus Kanturski & Wieczorek, sp.n. the setae of L. pallipes are much thicker and with brown pigmentation.On the other hand, the chaetotaxy of the body and the form and shape of the siphunculi clearly distinguish L. crassicornis from other Lachnus species.All setae of L. crassicornis are very thin and hair-like with pointed apices.Only the setae on the posterior parts of tibiae are slightly thicker and much longer than others.The setae on the dorsal part of the abdomen are almost identical with the setae on the ventral side.Probably the long, hairlike and pointed setae on the ventral side of the abdomen and the same host plant were the reasons why the slides of L. pseudonudus sp.n. were wrongly determined by Canakçioglu as L. crassicornis and the latter was listed in the aphidofauna of Turkey by the author (Canakçioglu 1966(Canakçioglu , 1967(Canakçioglu , 1975)).Dorsal setae of L. pseudonudus sp.n. are extremely short and inconspicuous, so they probably were overlooked during the examination of the material.However, the shape of the siphunculi, as well as the very well-developed flange with reticulation and other distinctive morphological and biometric features (see Similarly, L. chosoni is a rare aphid species, which is known only from the type locality in Myohyang-san (Korea) and all material, including the types, comprises three apterous viviparous females.Although Szelegiewicz (1975) provided a detailed description and drawings of this species, its taxonomic position was undermined and it was treated as a synonym of L. pallipes (Blackman andEastop 1994, 2014;Remaudière and Remaudière 1997).On the other hand, Binazzi and Remaudière (2010) gave L. chosoni full species status.However, the authors underlined that it was keyed only on the basis of the data from the original Szelegiewicz's description without studying the type material and still there were doubts about the possible synonymy of these species.A comparison of the type material of L. chosoni and L. pallipes from various localities, biometric ratios of the lengths of antennal segments, the apical segment of the rostrum and the hind tarsus clearly show differences between those species (see Table 3).Moreover, L. chosoni is characterised by the larger siphuncular sclerite diameter, different colouration of the hind tibiae and, most conspicuously, very small mesosternal tubercles (Figs 3c,g,i).Species belonging to the "pallipes" group, including L. pseudonudus sp.n., are characterised by the absence of those structures, unlike the remaining Fagaceae-feeding species of the genus Lachnus (especially the Quercus spp.habitants, Özdemir et al. 2005), which have prominent mesosternal tubercles.However, the presence of longer and shorter setae on hind tibiae, which is also a unique character of the "pallipes" group, indicates a close relation of L. chosoni with this group of species.

Table 2 .
The main morphological and biometric differences among Lachnus crassicornis and L. pseudonudus Kanturski & Wiec- zorek, sp.n.BL-body length, HLL-hind leg length, AL-antennae length, ANT VI-antennal segment VI length, ANT III-antennal segment III length, HT I-first segment of hind tarsus length, HT II-second segment of hind tarsus length.CharacterLachnus crassicornisLachnus pseudonudus Kanturski & Wieczorek, sp.n.Dorsal chaetotaxyThorax and abdomen very densely covered by very thin, fine and pointed setae, 0.037-0.050mm long Thorax and abdomen covered by very short, inconspicuous setae, arranged in 3-4 rows on each segment with blunt, capitate,

Table 3 .
The main morphological and biometric differences among Lachnus chosoni and L. pallipes.

Table 2 )
(Binazzi and Remaudière 2010 and separate taxonomic position within the genus Lachnus.Both L. crassicornis and L. pseudonudus sp.n. are known from single localities.L. crassicornis was recorded only from two localities in Israel, Daphne and Hotshat(Binazzi and Remaudière 2010; the record of this species from Q. robur in Romania reported by Holman and Pintera 1981 needs confirmation) whereas L. pseudonudus sp.n. is only known from its type locality in Turkey.The available material confirms the same host plant for both species: Q. ithaburensis (Decne).The Tabor oak includes two subspecies -Q.ithaburensis subsp.macrolepis (Kotschy) Hedge & Yalt.and Q. ithaburensis Decne.subsp.ithaburensis.These two subspecies of the Tabor oak occur separately in two Mediterranean subregions i.e.Q. ithaburensis subsp.ithaburensis is known only from Israel and north-western Jordan, whereas Q. ithaburensis subsp.macrolepis occurs in the western part of Turkey and in an enclaved region eastward to Ankara (Drufour-Dror and Ertas 2004).As the two subspecies of the Tabor oak do not overlap in their occurence it is argued that L. crassicornis is asso- ciated with Q. ithaburensis subsp.ithaburensis, and L. pseudonudus sp.n. with Q. ithaburensis subsp.macrolepis, which additionally corroborates the separateness of those two species.