Conochironomus

Cranston, Peter S., 2016, Conochironomus (Diptera: Chironomidae) in Asia: new and redescribed species and vouchering issues, Zootaxa 4109 (3), pp. 315-331 : 327

Definition and recognition of Conochironomus

Distinctive adult males provided the basis for recognition, originating with Freeman’s (1961) observation that some African species of Endochironomus were aberrant. Since erection of the genus ( Freeman 1961), the adult male continues to provide strong evidence for generic distinction. As stated by Cranston & Hare (1995), amongst taxa in which the male has 13 flagellomeres, lacks acrostichal setae and there is no spur on the anterior tibial apex, the conical shape of the tibial spurs is uniquely diagnostic. In Cranston et al. (1989), Conochironomus males possessing median volsellae would key to Paratendipes ; those without median volsellae key to Stictochironomus . Microtrichia extending onto the anal point ( Fig. 2 A–C) are distinctive. Saether (1977: 160) keyed female Conochironomus with a diagnostic combination of rounded anterior tibial apical scale, conical mid and hind tibial combs each with spur, six flagellomeres, lack of acrostichals, and gonapophysis VIII with ventrolateral lobe smaller than dorsomesal lobe. The latter observation reflects a higher level of variation in female genitalia in some taxa than documented by Saether (1977), as exemplified in closely related Polypedilum species ( Cranston et al. 2016).

Regionally, pupal Conochironomus can be recognised by having few (6–8) branches to the thoracic horn, no pedes spurii A, and an unusual, perhaps unique organisation of lateral setae, with the LS fine and short on segments V and VI and anteriorly on VII, and with taeniate LS3, 4 on VII and all LS1–5 on VIII. The posterolateral corner of VIII (‘comb’) in Conochironomus with few to several small teeth is somewhat distinctive and varies specifically.

Larval Conochironomus appear well-characterised by a six-segmented antenna with Lauterborn organs in alternate apical positions on the second and third segments, and by the distinctive median mentum with four (ventromental) teeth that protrude relative to the lateral, dorsomental components. In the Holarctic key ( Epler et al. 2013) the separation suggested in couplet 9 based on colour intensity of mandibular and mental teeth may not always work in practice, at least outside the Holarctic where there is greater diversity of the corresponding taxa. The arrangement of the median mental teeth in Conochironomus and the relative length of the antennal flagellum resemble the conditions in some Paratendipes but this genus differs in the pecten epipharyngis that comprises only 3 simple teeth. In Stictochironomus , the Australian S. fluviatilis (Skuse) and S. illawara Freeman fail to conform to the Holarctic diagnosis ( Cranston 1996), and regionally Imparipecten Freeman and Afro-Australian Skusella Freeman also must be considered ( Cranston 1996). Perhaps the only consistent feature differentiating larval Conochironomus is the shape of the 3rd antennal segment, which is narrow basally alongside the basal Lauterborn organ, and more flared apically. There is an indication of this shape also on the 4th antennal segment beside the apical Lauterborn organ.

Figures

FIGURE 2. Conochironomus spp., adult genitalia. A. C. nuengthai sp. n., Male, left side dorsal, right side ventral; B. C. sawngthai sp. n., Male, left side dorsal, right side ventral stylised; C. C. tobaterdecimus (Kikuchi & Sasa), Male, dorsal, and superior volsella, ventral (inset, detail); D. C. tobaterdecimus (Kikuchi & Sasa), Female genitalia, (partial, ventral).