Reed beetle ID

NickU · #1 (**permalink**) 10-06-2011, 04:26 PM

Does anyone know what species these ? Reed beetles ? are. Thought they were small longhorns at first, but am pretty sure they're Chrysomelid reed beetles.

I'm guessing they're the common Donacia semicuprea (or are the beetles in my pics too slim?), rather than the much rarer Donacia aquatica which may not even be found in my area, or maybe there are other spp. they could be.

There were lots around, on tall broad bladed grasses of some kind (maybe Reed Sweetgrass Glyceria maxima, which is D. semicuprea's host plant, but I'm no botanist and there were only laves to go on).

May 4th 2011 c8mm on riverbank vegetation, Wiltshire. Always trying to hide behind the plants or flying off when I got close... Mating pair a bit easier!

Nick Upton - naturalist / photographer

artdemole · #2 (**permalink**) 11-06-2011, 12:26 PM

Maybe Donacia crassipes...

NickU · #3 (**permalink**) 11-06-2011, 08:36 PM

Many thanks for the suggestion, but I read that D. Crassipes is the Water lily reed beetle and only feeds on water lilies, and there are none in the river where mine were. D. crassipes also seem to have wider back legs with spines and mine don't. Now I've checked further, it seems there are a number of Donacia spp. in the UK, all quite similar. The key may be to know what is is they are feeding on, as many are quite specific. Shame my botany isn't better.. I went back to the river today, though and got a better shot, and think the plants thye are on must be some kind of sedge or rush: they are standing in the river and are big, tough leaves (still no flowers). I THINK the most likely beetle species is actually Donacia vulgaris, as it looks just right, is common and widespread and the distribution extends to Wiltshire and it's usually on bullrushes and reeds according to ths link:

Donacia vulgaris

No doubt, to be sure it would take a real expert on this group who'd probably need a specimen to be sure, so it may just have to be Donacia sp. maybe vulgaris for now!... unless an expert can confirm/ correct me.

Today's pic. Lots were mating.

Fauna · #4 (**permalink**) 11-06-2011, 10:02 PM

Have you got a photo of the top of these beetles, need to see the pronotum and colour of elytra.

D. vulgaris, D. semicuprea and D. simplex will be your likely options. You can also check them against the specimens on this site. Chrysomelidae (leaf beetles) Germany photo overview - kerbtier.de

In short....

D. semicuprea will have a groove on the mid line of pronotum.

D. vulgaris will mostly have colourfull bands running either side of the elytral suture. (also lack the groove on pronotum)

D. simplex won't be any of the above.

Regards Chris...

NickU · #5 (**permalink**) 12-06-2011, 10:03 AM

Many thanks Chris, some very helpful pointers. Yes I do have some dorsal views, and on the basis of these I think the beetles must be Donacia semicuprea as there does seem to be a groove in the pronotum (visible with some angles of light when focus sharp on that point) and the colour on the elytra seems more uniform than on D. vulgaris, though these iridescent beetles do look so different at different angles, so that's hard to be sure of. D. semicuprea is listed for Wiltshire. I'm still not sure the plant I find them on is Reed sweetgrass, which is listed as the only food plant by a few sources, but maybe it is. Old beds apparently often don't flower and do grow standing in water. Best top views with hints of pronotal groove attached.

Fauna · #6 (**permalink**) 12-06-2011, 12:31 PM

I think i may have been a bit misleading, should have said...

D. semicuprea will have a strong groove on the mid line of pronotum. (others may have a faint groove)

Having the specimen in hand would make me more confident, but i would be more inclined to go with D. simplex with these. The groove looks faint, also the elytra does not look broadened in the middle as you would see in D. semicuprea ?

Regards Chris..

NickU · #7 (**permalink**) 12-06-2011, 01:29 PM

OK, thanks again. Yes the grooves are very faint and the elytra may not broaden enough for D. semicuprea and everything looks right for D. simplex, which has quite a broad host plant range and is common and widely distributed and found in Wilts. A tricky genus, but I think we got there on this in the end!