Pemphigus bursarius is an aphid which causes pouch galls to form in the petioles of the leaves in some species of Poplar. The galls are seen more often than the aphid, and are 15 x 6 to 8 mm and form on one side of the petiole opening in June to release aphids. They start off yellowy green and become quite red later.

Gall Adult

On Black Poplar (Populus nigra) or its hybrids such as Lombardy Poplar (Populus nigra Italica)

The galls may be visible whenever the host Poplars are in leaf.

Poorly recorded with most records coming from the southern half of Britain.

Uncommon or under recorded in Leicestershire and Rutland. The Sapcote record of 2nd August 2014 appears to be only the second record for VC55.

https://influentialpoints.com/Gallery/Pemphigus_bursarius_Poplar-lettuce_gall_aphid.htm