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Uroleucon jaceae

Large knapweed aphid

Identification & Distribution 

Identification & Distribution:

Uroleucon jaceae is a large blackish aphid. The abdominal tergites 2-4 often have small marginal tubercles about the size of hair bases. The femora have the basal half pale and distal half dark, with a rather sharp transition between them. The tibiae are totally black. The siphunculi are reticulated over the distal 0.16-0.27 of their length and are 1.3-1.8 times the length of the cauda. The cauda is dark and bears 18-30 hairs. The body length of Uroleucon jaceae apterae is 3.0-4.5 mm long.

The clarified slide mounts below are of adult viviparous female Uroleucon jaceae : wingless, and winged.

Micrographs of clarified mounts  by permission of Roger Blackman, copyright AWP  all rights reserved.

The large knapweed aphid lives on various knapweeds (Centaurea spp.) and a few other species of Asteraceae.

Acknowledgements

Our particular thanks to Roger Blackman for images of his clarified slide mounts.

We have made provisional identifications from high resolution photos of living specimens, along with host plant identity. In the great majority of cases, identifications have been confirmed by microscopic examination of preserved specimens. We have used the keys and species accounts of Blackman & Eastop (1994)  and Blackman & Eastop (2006)  supplemented with Blackman (1974) , Stroyan (1977) , Stroyan (1984) , Blackman & Eastop (1984) , Heie (1980-1995) , Dixon & Thieme (2007)  and Blackman (2010) . We fully acknowledge these authors as the source for the (summarized) taxonomic information we have presented. Any errors in identification or information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure  provided by Blackman & Eastop (2006).

Useful weblinks 

 

Identification requests

Nigel Gilligan 11/10/2014

I found some aphids a while ago on Lesser (Black) Knapweed (I'm just starting to sort my annual stuff). It was 11th August.

Images copyright Nigel Gilligan, all rights reserved.

   

There appear to be 2 species, and I've identified them as
a) Uroleucon cirsii [first and second images, above]
b) U. jaceae [third image above]

In [the third image] you can see what I assume is the other species in the background.

Are these correct?

Bob, Influentialpoints:

  • Interesting aphids. You do seem to have two species here, but Uroleucon cirsii does not occur on knapweed. It is almost certainly Uroleucon jaceicola:

    Uroleucon jaceicola:
    Pale cauda, black siphunculi, pale legs with dark knees and tips of tibiae
    [first and second images, above] (foreground).

    Uroleucon jaceae
    Dark cauda, black siphunculi, black legs
    [second image above] (IV instar future alate in background), and [third image above].

    Uroleucon jaceae is very common but this is the first time we have seen Uroleucon jaceicola.

Nigel Gilligan 13/10/2014

Just an afterthought on this. Is "almost certainly " sufficient to record it as that species (maybe with a note to that effect), or not?

I've just had a similar experience with an unusual plant bug, where the specialist had never seen one before until this summer, so initially hedged his bets and said it "it looked like", but later said he was pretty happy about it ... it had to be that, etc. I do wonder whether determinations should come with a % confidence measure!

Nigel Gilligan 16/10/2014

Come across another Uroleucon jaceicola, on Knapweed, from the summer. Since it's unusual, two images attached [shown below]. Not great photos though.

Images copyright Nigel Gilligan, all rights reserved.

 

Did you reply to my query about whether I can actually log Uroleucon jaceicola from the previous images? The ones above are not good, I know, but I have several other images from the recent submission, with views of groups of them from different angles, but not actually more detailed views. There are some U. jaceae mixed in with them, I think.

Bob, Influentialpoints:

  • Just found some Uroleucon jaceicola in my own photos - perhaps it was a good year for them. Thanks for those extra piccies - yes you can certainly log them.