Range Extension for Orthocladius (Mesorthocladius) Nimidens Sæther (Diptera: Chironomidae) Based on Records from Missouri

Orthocladius (Mesorthocladius) nimidens was described by Saether (2005) from material collected in Ohio, and the species is reported also as O. (O.) sp. “Jacobsen” from North Carolina and Indiana (Epler 2001; Saether 2005). We collected specimens of O. nimidens larvae and pupae from 13 headwater streams in native tall-grass prairies in the Osage Plains Ecological Section of Missouri (Cleland et al., 1997; Nigh and Schroeder 2002) on 27 and 28 March 2008, and from 12 headwater streams in woodlands and grasslands in the Central Dissected Till Plains Ecological Section of Missouri (Cleland et al., 1997; Nigh and Schroeder 2002) on 7 March, 14 16 April, and 13 May, 2008 (Fig. 1). Our records of O. nimidens in Missouri represent the first for this species for the state and extend the known distribution of O. nimidens farther west in North America than documented previously in the literature. However, considering the recent description of this species and its apparent preference for headwater stream habitat, it probably has a widespread distribution. We sampled aquatic macroinvertebrate communities with 500 μm mesh bottom aquatic kick nets in riffles, pools, and submerged rootmats, and by using brushes with moderately stiff bristles to brush submerged woody debris into 500 μm mesh bags according to methods outlined by Sarver et al. (2002). Chironomid larvae and pupae were mounted on glass slides with CMCP-10 mounting medium, covered with cover slips, dried, ringed with clear nail polish, and were examined with a compound light microscope. Taxonomic keys and descriptive information provided in Coffman et al. (1986), Epler (2001), Saether (2005), and Ferrington et al. (2008) were used to identify specimens. Larvae of O. nimidens are characterized by a mentum with 7 or 8 lateral teeth, a broad median tooth, and secondary dissections of the bifid SI. Sometimes the SI dissections are strong and can be misleading when performing genus level identifications. It should be noted that the key provided by Epler (2001) is curVolume 121, Number 4, September and October 2010 329