Prociphilus sp. on Fraxinus excelsior

The gall is formed at the end of a twig. It happens that the twig continues its growth behind the gall, or not. On the picture below, one can note that the end is still alive but seems unable to develop, maybe because of the heavy pressure exerced by the numerous aphids hidden under the curled leaves.

Two species of the genus Prociphilus (Aphididae > Eriosomatinae > Pemphigini) produce this kind of galls on ashes, i.e. P. fraxini and P. bumeliae. The excellent Influential Points website (highly recommended about aphids in general) publishes a page about those taxa. One should note that those aphids build bird nests but may also appear as loose colonies on the stem of the host plant (see the pictures of this site). They lack siphunculi and are most of the time not ant attended.

After opening the nest, I could observe aptera of different stages, with a light pink-orange coloration of the abdomen. One can also note that the aphids reject honeydew in spheres whose wall is made of wax.

Here, alates in their juvenile form. One can see the alar pouches.

According to Influential Points, the taxa Prociphilus bumeliae and P. fraxini can only be distinguished at the alate stage produced in the leaf nest.