Illinoia thalictri

Adult apterae of Illinoia thalictri (see first picture below) are pale sea green to yellowish green, and faintly wax-powdered. Antennal tubercles are widely spaced, each with 3 hairs. Antennae are pale, except for the apices of the segments which are dusky, and segment VI which is dark. The antennae are 1.3-1.5 times the body length, and antennal segment III bears 1-7 secondary rhinaria on the basal 0.17-0.67 portion. The longest hairs on antennal segment III are about 0.5 times the basal diameter of that segment. The rostrum reaches to between the middle and hind coxae, with the apical rostral segment about 0.83 times the second hind tarsal segment. The legs are pale to slightly smoky, with the tips of tibiae slightly darker and tarsi much darker; the first tarsal joints have 5 hairs. The siphunculi are pale to dusky, in some specimens with the swollen area slightly darker. The siphunculi are 0.18-0.33 times the body length, with the apical 0.08-0.13 portion of the siphunculi reticulated; they are swollen over the distal 0.25-0.50 portion up to 1.2-1.7 times the smallest diameter basally. The cauda is conical, about 0.38-0.44 times the siphunculi, with 3 pairs of lateral and 1 dorso-apical hair. Body length of adult Illinoia thalictri apterae is 2.0-2.3 mm.

Note 1: The descriptions and ranges given above are based on a small sample (n=3).
Note 2: Blackman, in Aphids on Worlds, plants suggested that another of Andrew Jensen's images of an aphid on Thalictrum (see second picture below), labelled by Jensen as 'Illinoia corylina?', is also Illinoia thalictri. It is reddish rather than green, but several Illinoia species have both red and green forms.

Images above copyright Andrew Jensen under a creative common licence.