Considerations on systematics, morphology and bionomics

Some taxa collected in the present study deserve systematic, morphological or bionomic comments, which are described below:

Apedilum sp. The genus Apedilum is currently known by three species: A. elachistum, A. subcinctum of the Neotropical region (Epler 1988) and A. griseistriatum endemic of the Subantarctic forest (Donato et al 2015). The larvae of Apedilum collected during the present study, do not fit in any of these species. In the Apedilum sp. larvae, the dorsal and the apical teeth of the mandible are the biggest for the genus; the 9 teeth of the pecten epipharyngis are triangular and with about 100 maxillary plate striae on the ventromental plate. The knowledge of the different life stages of this morphotype will clarify if it belongs to a new species.

Cricotopus -Paratrichocladius conflict. Since the erection of the orthoclad genus Paratrichocladius Santos-Abreu, separation in any life stage from the cosmopolitan, diverse Cricotopus Wulp has been problematic. In the first detailed revision of Cricotopus (Hirvenoja 1973), mainly western Palearctic species were included and delimitation of species groups was made. Later, difficulties with species groups outside the western palearctic were recognised.Following Cranston et al (1983), the larva of Paratrichocladius is distinguished from Cricotopus by the mentum with first lateral teeth constricted at base appearing wider in the middle than at bottom, by the smooth outer margin of mandible, by the lack of body setal tufts and by the presence of an internal seta in the mandible. Epler (2001) noted that it is not possible to separate many species of Orthocladius larvae from those of Cricotopus and/or Paratrichocladius. The clearest difference between the last two genera is in the male adults, where Paratrichocladius would be distinguished from Cricotopus only by the dorsocentral setae arising from small pale pits rather than direct from the cuticle as in Cricotopus (Hirvenoja 1973).

In a taxonomic review of the genus Cricotopus from Australia (Drayson et al 2015), difficulties in separating the Paratrichocladius larvae from some of those of Cricotopus was also exposed, especially when the specimens have l4 setal tufts on abdominal segments. These authors noted that particular problems in Australia stem from the close resemblance of the larvae of C. brevicornis to some larvae associated by rearing -as well as by DNA- with adults possessing dorsocentral setae that arise from pale areas (i.e. conforming to Paratrichocladius). At the same time, Cranston & Krosch (2015) performed a molecular analysis of Cricotopus and Paratrichocladius from Australia, concluding that Paratrichocladius is a subgenus of Cricotopus.

During the identification of larvae collected, Paratrichocladius was a separate genus of Cricotopus and we considered that the larvae with the first lateral tooth of the mentum being broader in middle than at the base belongs to Paratrichocladius following Cranston et al (1983). After the publications cited above, we identified those Paratrichocladius larvae as a subgenus, but we are conscious that this could be incorrect due to the problem above mentioned. Hence, the reared material and/or DNA associations are required in order to solve possible problems similar to those found by Drayson et al (2015).

Diamesinae. The morphotypes of Diamesinae collected in the present study belong to the Heptagyiini tribe. This tribe is austral and well-defined in all life stages, however it is not possible yet to distinguish the larvae to genus level with any confidence. This is due to the scarce reared associations being unclear which characters are reliable. The 'distinctive' collar (occipital margin of the head) apparently is a feature only of the fourth instar larva (Cranston 2010). We took into account differences in the mentum teeth arrangement to distinguish the different morphotypes of Diamesinae.

Macropelopiini sp. This Tanypodinae tribe is commonly found in cool seeps, springs, and small streams. The larvae of Macropelopiini collected in the present study share with Paggipelopia and Apsectrotanypus the dorsomental plates with low number of teeth. However, these larvae differ by the straight inner lateral teeth of the ligula.

nr. Bryophaenocladius. This morphotype keyed in the identification key of Epler (2001) in the dilemma Gymnometriocnemus - Bryophaenocladius. Based on the possession of non divided posterior parapods, this larva fits in Bryophaenocladius except for the presence of 5 lateral teeth in the mentum. Based in the number of lateral teeth in the mentum, and because Bryophaenocladius was defined as predominantly terrestrial/semiterrestrial with the only aquatic record for B. subvernalisfrom alpine European lakes, we doubted to include this larva in this genus and was considered tentatively as nr. Bryophaenocladius.

nr. Psectrocladius. A single larva fits with Psectrocladius in the larval key of Cranston et al (1983) and Epler (2001), except for the absence of cardinal beard in this larva and by the presence of 6 lateral teeth in the mentum. This morphotype could be assigned to Parapsectrocladius, but the possession of one wide median tooth in the mentum resembles Psectrocladius instead of Parapsectrocladius that has two median teeth in the mentum. For these reasons, we refer this single larva as nr. Psectrocladius.

nr. Riethia. A single Chironominae larva could not be keyed in any known genus. We named it as nr. Riethia by its resemblance with that genus, a mentum with the first lateral teeth long, second lateral teeth short, and the remaining outer four on an even line of slope. However, this larva clearly differs from Riethia by the double median teeth, ventromental plates widely separated medially, spinosus-like pecten epipharyngis and coloration of mandible.

Podonomus spp. There is an important gap, even at genus level, in the knowledge of Podonominae larvae, and commonly it is not possible to identify the larvae of Podonominae at specific level. The presence of mature larvae in which the thoracic horn of the pupa is observed, sometimes helps identification at specific level. The scarce knowledge of the Podonominae larvae, does not allow us to identify each of the three morphotypes at specific level.

Stictocladius sp F. It refers to the chilean morphotype described by Saether & Cranston (2012). In December, this species was collected in high densities at sites from I to V and, in low densities in site VI, while it was collected only in site I in February. This distribution with a higher altitude preference could be responding to cold-stenothermal requirements for the species.

In the qualitative study from the same area, we collected male pharate adults of Stictocladius acrilobus Sæther & Cranston and Botryocladius edwarsi Cranston & Edward. Further taxonomic studies and the rearing of larvae from the Challhuaco-Ñireco river system will possibly allow us to elucidate the systematic problems of chironomids and therefore lead to an increase in the number of taxa recorded in this study.

REFERENCES

Cranston PS, Oliver DR, Sæther OA (1983) The larvae of Orthocladiinae (Diptera: Chironomidae) of the Holarctic region -Keys and diagnoses. In: Wiederholm T (ed) Chironomid of Holarctic region. Keys and Diagnoses. Part 1. Larvae. Lund, Sweden pp 149–291.

Cranston PS (2010) Lucid key to Larval Chironomidae. [Internet]. [cited 2014 October]. Available from:

Cranston PS, Krosch MN (2015) DNA sequences and austral taxa indicate generic synonymy of Paratrichocladius Santos-Abreu with Cricotopus Wulp (Diptera: Chironomidae). Systematic Entomology 40(4):719–732.

Donato M, Siri A, Massaferro J, Brooks SJ (2015) Apedilum griseistriatum comb. nov., placement of Chironomus (Polypedilum) griseistriatum (Diptera, Chironomidae). Iheringia. Serie Zoologia 105:5−11.

Drayson N, Cranston PS, Krosch MN (2015) Taxonomic review of the chironomid genus Cricotopus v. d. Wulp (Diptera: Chironomidae) from Australia: keys to males, females, pupae and larvae, description of ten new species and comments on ParatrichocladiusSantos Abreu. Zootaxa 3919:1−40.

Epler JH (1988) A reconsideration of the genus Apedilum Townes, 1945 (Diptera: Chironomidae). Spixiana 14:105–116.

Epler JH (2001) Identification Manual for the Larval Chironomidae (Diptera) of North and South Carolina. A guide to the taxonomy of the midges of southeastern United States, including Florida. Special Publication. North Carolina Department of Environmental and Natural Resources: Division of Water Management. Raleigh, North Carolina.

Hirvenoja M (1973) Revision der Gattung Cricotopus van der Wulp und ihrer Verwandten (Diptera, Chironomidae). Annales Zoologici Fennici 10:361–363.

Sæther OA, Cranston PS (2012) New World Stictocladius Edwards (Diptera: Chironomidae). Neotrop. Entomol. 41:124–149.