Eriophyes serotinca Beut.

Chadwick's No. 100

Host Prunus serotina Ehrh.

This is a club-shaped gall, produced on the upper side of the leaf of the host. The aperture of exit, which is on the lower side, is surrounded by fine white hairs. It varies in length from 5 to 8 mm. and at a distance from the apex of about two-thirds the total length, it is narrowed into a stalk with an average diameter of 1 mm. In color it varies from green to a distinct red.

The stimulation has not produced very marked changes in the structure of the leaf near the origin of the gall. Apart from the fact that the spongy parenchyma has divided more actively, the mesophyll is normal. The upper epidermis of the leaf that forms the outer covering of the gall, has its cell walls abnormally thickened. The lower epidermis that lines the gall cavity has larger cells than the unstimulated epidermis, and from these cells originate elongated, unicellular trichomes with bulbous bases. The hairs on the normal leaf are acicular and unicellular. While the cells in the neck of the gall are arranged in rows parallel to its length, the larger cells that form the main body of the gall are not regularly placed. The vascular strands pass up from the leaf at a distance of about three cell layers from the gall cavity.

This is a striking and impressive pouchtype gall that appears on the upper surface of the leaf. Each gall is elongate, spindle shaped, about 4-8 mm long, with a pointed or attenuate tip, and is attached to the leaf blade by a slender stalk. The galls are solitary and tend to crowd, often particularly on the basal part of the leaf, mostly near the midrib. They vary from yellowish green to brownish, to reddish. The interior of the gall, where the mites are found, is hollow, with fleshy, turgid tissue. When mature, the galls split open longitudinally, dispersing the mites.

Specimens have been found only on blackcherry in the Eastern United States. Phytoptus cerasicrumena is not likely to be confused with other species that infest Prunus. The galls induced by this mite are distinctive.