"Riffle beetle" - Stenelmis

Moved

… Tim Moyer, 4 November, 2010 - 3:17pm

Moved - Thanks Crystal

… Tim Moyer, 22 February, 2010 - 12:17am

Be careful! This specimen is

Be careful! This specimen is not Stenelmis sinuata. Stenelmis sinuata has testaceous maxillary palps and antennae and this one has black antennae (well, actually they are kind of two-toned). Also, the locality for this individual is well out of the range of Stenelmis sinuata (it's a southern species) and it is much more likely to be either S. musgravei or S. quadrimaculata. Again, it's tough to say which without genitalia, so I'd say just keep it at Stenelmis sp.

… Crystal Maier, 21 February, 2010 - 11:01pm

Missed this comment...

thanks for the correction...

… Tim Loh, 1 March, 2010 - 11:28am

Moved

Moved from Stenelmis quadrimaculata.

… Tim Loh, 8 January, 2010 - 6:58pm

Moved

Moved from Riffle Beetles.

… Tim Moyer, 20 January, 2008 - 11:16pm

rather, Stenelmis crenata

upon further review, this is probably Stenelmis crenata (the 5th tarsi seems clearly longer than others combined)

… Tim Moyer, 23 December, 2006 - 1:35am

Probably quadrimaculata

You had it right the first time, well actually, you also had the key right too, just the wrong species. The Humerosa-sinuata group (which S.quadrimaculata is in) has the 5th tarsi distinctly longer than the rest combined. The Crenata group, on the other hand, has the 5th tarsi that are NOT distinctly longer than the rest combined. This is most likely S. quadrimaculata,judging from where you found it. However, The key couplet that splits S. quadrimaculata from S. musgravei involves genitalia, so you won't be able to get a definitive answer without pulling the genitalia out. Try using

Brown,H.P. 1976. Aquatic dryopoid beetles (Coleoptera) of the United States. EPA Water Pollution Control Research Series

I hope that this helps!

… Crystal Maier, 9 January, 2007 - 9:29am

thanks Crystal

I was keying using Downie and Arnett's Stenelmis key which they state "from Sanderson, 1938". It appears the first cuplet may be reversed or at least inaccurate. 1a: "last tarsomere distinctly longer than 4 preceding combined, last usually abruptly dilated beyond middle; claws robust." leads to; sexlineata, crenata, lateralis, concinna, sandersoni, mera, and bicarinata.

I found your Brown '76 reference on EPA's site and posted the link on the Elmidae family Guide info page.

Given all this, would you please check my image post for S. bicarinata to see if I missed this ID too?

Thanks!
Tim

… Tim Moyer, 9 January, 2007 - 3:35pm