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Scolytinae - Scolytus rugulosus

Scolytinae - Scolytus rugulosus
Roseville, Vernon St., 38.7227, -121.2993. Elevation = 50m (164'), Placer County, California, USA
April 24, 2019
Size: 3.2 mm
Lindgren Funnel Trap. I Can't key to a genus that looks right. Help with ID would tell me where I'm making a mistake in Arnett's keys. I've been getting one or 2 of these every night in my trap whenever the temp is good around and after sundown this spring so it must be common.

Characters as I perceive them.
-- Visible from above.
-- Eye is linear.
-- Antennal club has sutures that are procurved.
-- Can't determine how many segments are in the funicle.
-- Lateral ridge does not extend to the forward edge.
-- Looks like the indentations are longitudinally strigose.
-- Protibial curved process - can't find that it is bifid as the key asks for.
-- Picture is of the metatibia.
-- Anterior margins of elytra procurved, with large scutellum.

Images of this individual: tag all
Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus Scolytinae - Scolytus rugulosus

Hey Glen
Unfortunately you went astray at the very first couplet! This couplet can be easily misinterpreted. The "head visible" part especially. Often with trapped beetles, the head gets extended in a way that it appears visible from above. Even at rest, this genus has its head slightly visible. I think the couplet should read "usually visible..." but anyway. The part about the basal margin of the elytra being procurved and bearing crenulations is really what I tend to stress when teaching people this key. For Scolytus, its not quite as obvious because they have such a large scutellum, but the margin on either side of the scutellum is straight, and there are no crenulations.

Better seen here:

as opposed to procurved and crenulate as seen here:

That takes you to couplet 24: the single curved process on the anterior and posterior tibiae... or otherwise. You noticed this on your specimen and got a great shot of it.

Then couplet 25 gets you to genus pretty easily.

Smith and Cognato (2014) (1) would be the best resource for keying Scolytus to species. This one comes out in the first couplet, as it's the only one in the nearctic fauna with narrowly rounded elytral apices.

Excellent help. Thanks. W
Excellent help. Thanks. Wondered about the straight pronotum, but thought no asperites and extended head pushed it the other way (which of course were variable). Arnett's key edited and will help a lot.
I wish more people would state reasons they decide what taxon something should be. Great teaching forum when used that way.

You’re welcome
I tend to provide a bit more ID info when it’s clear the person is making an effort and using keys to try to identify something, or made an incorrect guess. I agree that this is one of the most valuable things about this website.


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