Aphid colonies occur on the undersides of sycamore leaves. Alates with closely spaced, black, abdominal cross-bars and black pterostigmata. White "dimorph" nymphs in dense groups.

Please provide close-up images of the aphids and state the host species.

Periphyllus acericola may be found anywhere that Sycamore is present.

Aphid colonies may be found when Sycamore is in leaf.

True status in Britain is difficult to determine due to lack of records.

Status in Leicestershire and Rutland not known.

https://influentialpoints.com/Gallery/Periphyllus_acericola_Sycamore_Periphyllus_Aphid.htm