Apedilum griseistriatum comb. nov., placement of Chironomus (Polypedilum) griseistriatum (Diptera, Chironomidae)

The study of the type material of Chironomus (Polypedilum) griseistriatum Edwards, 1931 described from Patagonia lead us to formally transfer the species to Apedilum Townes, 1945 as a new combination, and a reared specimen allows us to describe its pupa. Based on several larvae belonging to Apedilum collected in the proximity of the localities in which the adults and pupae were found, we tentatively describe the larval stage. Subfossil larval head capsules of the same species were found in Laguna Stibnite at 46°S in Chile dated to about 2,500 years ago and in Puerto Blest, Lago Nahuel Huapi at 41°S in Argentina dated about 2,000 years ago. We discuss the habitat of the species based on both modern and subfossil material. Identification keys to male adult, pupae and fourth instar larvae are also provided.

The genus Apedilum was first described by Townes (1945) to include two species, A. elachistum and A. subcinctum.In the same work, the author established that Chironomus nigrohalteralis Malloch, 1915 and Chironomus (Lauterborniella) brachylabis Edwards, 1929 were synonyms and proposed a new combination, Apedilum nigrohalterale (Maloch).Previously, Lenz (1941) had proposed the genus Paralauterborniella for Chironomus (Lauterborniella) brachylabis.Roback (1957), in a footnote in a key, mentioned Lenz's 1941 paper and considered Apedilum a junior synonym of Paralauterborniella. epLeR (1988), based on characters from all life stages, resurrected the genus Apedilum as a legitimate genus made up of two species, A. elachistum and A. subcinctum.Consequently, Paralauterborniella became a monotypic genus.
Apedilum is widely distributed in North and South America.The species A. subcinctum occurs in the Nearctic region and A. elachistum is present in the Nearctic and Neotropics.Recently, DonaTo et al. (2008) analyzed the geographical variation of A. elachistum.
Our re-examination of the type material of Chironomus (Polypedilum) griseistriatum described by eDwaRDs (1931) from Patagonia lead us to formally transfer this species to Apedilum as a new combination and reared specimens allow us to describe its pupa.Based on several larvae belonging to Apedilum collected in the proximity of the localities in which the adults and pupae were found, we tentatively describe the larval stage of this species.Subfossil head capsules of Apedilum were recovered from sediment cores from several shallow lakes.We compared these morphotypes with the modern specimens of Apedilum found in northern Patagonia.

MATERIAL AND METHODS
The type material of Chironomus (Polypedilum) griseistriatum is deposited in the Natural History Museum, London (NHM, UK).The holotype male is pinned with its hypopygium mounted in Canada balsam and the male paratype is mounted in Euparal.The new specimens we have studied are deposited in Museo de La Plata (Argentina, MLP), Programa de Estudios Aplicados a la Conservación de la Biodiversidad (CENAC/APN) and NHM.
The morphological nomenclature follows saeTheR (1980) and epLeR (1987).All measurements in this study are in μm unless stated otherwise and are given as ranges followed by the measurement of the paratype.Diagnosis.The male of Apedilum griseistriatum is clearly differentiated from the rest of the species of the genus by having the wing without pale spots, anal point always present with its length greater than the maximum width of superior volsella and gonostylus greatly inflated.The pupa of A. griseistriatum is separated from the rest of the members of the genus by the absence of shagreen on T VII and VIII and dorsal shagreen on T II-VI subquadrate with its median area bare.The presence of 74-81 maxillary plate striae on the ventromental plate separates A. griseistriatum from the rest of the larvae of the genus.
Remarks.Subfossil head capsules of Apedilum were recovered from sediment cores from Laguna Stibnite (46°S, Chile) and Lago Nahuel Huapi, Blest branch (41°S, Argentina).The 11 m core covers the period from the present to about 17,000 calendar years ago.Apedilum was found at ca. 2 m depth matching an age of 2,500 calendar years old.In Lago Nahuel Huapi, fossil specimens of the genus were found in several samples of a 2,000 years BP core.After the comparison of these morphotypes with the modern specimens of Apedilum found in northern Patagonia, we concluded they are the same species.The abundance of fossil head capsules from the lake sediment sequence were insufficient to make any interpretation about its ecology, however the species was found associated with Limnophyes, Labrundinia, Chironomus and Parachironomus (MassafeRRo & bRooks 2002).In that study, the presence of these littoral/warm assemblages was interpreted as a change in the water level caused by a decrease in the precipitation regime.Likewise, in Lago Nahuel Huapi, fossil Apedilum was found in littoral areas together with orthoclads such as Limnophyes, Chaetocladius and Cricotopus.In northern Patagonia (41°S) Apedilum was found in modern samples of Lago Los Clavos (1200 m a.s.l.), Lago Nahuel Huapi shore near Puerto Blest, Lago Gutierrez, Lago Espejo (ca.800 m a.s.l.) and Lago Futalaufken (900 m a.s.l.).These lakes are located in the Subantarctic province following the biogeographic schemes proposed by cabReRa & wiLLink (1973).This biogeographic province has a strong precipitation gradient from west to east, with about 5,000 mm per year in Chile and 700-800 mm per year in Argentina due to the influence of the Andean Cordillera.These findings suggest the new species prefers littoral zones of deep lakes such as Nahuel Huapi and Gutierrez and shallow lakes such as Los Clavos.Further studies are needed to understand fully the ecological requirements of this species.DISCUSSION eDwaRDs (1931) described griseistriatum in the subgenus Chironomus (Polypedilum) together with the species quinquesetosum according to the current classificatory system for that time.spies & Reiss (1996) transferred quinquesetosum to the genus Polypedilum Kieffer and recently this species was placed in the subgenus Polypedium (Tripodura) by fuenTes & DonaTo (2014).The new combination Apedilum griseistriatum proposed here is based on the possession of this unique combination of diagnostic male characters for the genus Apedilum that is: antennae with 13 flagellomeres, apex of fore tibia truncated, squama bare and superior volsella globose.
The pupa of Apedilum is difficult to diagnose between those Chironomini pupae with few branches on the thoracic horn.In the identification key of coffMan & feRRingTon (1996), Apedilum keys to Stelechomyia Reiss because is erroneously described as having cephalic tubercles (Jacobsen, 2008). cRansTon et al. (1989) does not include Apedilum, but in a pass through their key  (1988,1996), Paralauterborniella is separable by presence of cephalic tubercles and a blunt nose on the wing sheath; Zavreliella by the presence of cephalic tubercles, presence of paired patches of short points on tergites II-VI, and 4 lateral setae on T VIII; and Oukuriella by the presence of wrinkled cephalic tubercles and 4 lateral setae on T VIII.
The tentative larval stage proposed in this study for A. griseistriatum comb.nov.possess the diagnostic combination of characters for the genus Apedilum: S I with bases fused medially; S II with short basal segment; pecten epipharyngis a single plate; 6 segmented antenna, with alternate Lauterborn organs; mentum with pale bifid median tooth, and first lateral teeth reduced and adpressed to larger second lateral teeth; well developed maxillary plate striations; and mandible with dorsal teeth (epLeR, 2001).
Apedilum griseistriatum comb.nov.has almost all the characters described by epLeR (1988) as diagnostic for Apedilum but there are some additional characters which emend the diagnosis for the genus.Such characters are: the adult male has wing length 1.1-2.47mm, superior volsella with microtrichia dorsally and ventrally or without microtrichia, the gonostylus moderately to strongly inflated, sensilla chaetica present on the metatarsus of the middle leg, confined to apical 1/5, and sometimes present on apical 1/5 of hind metatarsus, or absent on all metatarsi.The larva has a greenish-gold or red body in life.
Within the genus, A. griseistriatum comb.nov.appears most closely related to A. subcinctum since in both species the caudolateral comb of T VIII in the pupae consists in a group of small spurs.In the adult of both species, the wing is not spotted and in A. griseistriatum comb.nov.an anal point is present but in A. subcinctum the anal point may be well-developed or absent.