A midge belonging to the genus Blaesodiplosis induces galls on the leaves of a shrub commonly called serviceberry (Amelanchier alnifolia). The hairy, white galls have red tips and are monothalamous (have only one chamber). The galls occur on the upper surface of the leaves and often occur close together in such numbers that they look like a hairy white mass and completely cover the leaf.
Midge eggs hatch several days after being deposited on the surface of a serviceberry leaf. As the larvae begin to feed on the plant tissue gall formation commences. The larva complete their development and pupate in the gall chamber. After pupation, the adult midges emerge and begin the cycle anew. A larva can be seen in one of the photographs.
Blaesodiplosis midges have no chewing mouth parts and only suck nutrients from the host cells lining the gall chamber. As a result the larvae do not destroy the plant tissues and only cause mild necroses which weaken, but do not directly kill, the serviceberry host. It is difficult to believe the midge larvae are not killing some heavily infected plants.
These woolly leaf midge galls were photographed on serviceberries growing on Fox Mountain (Modoc Forest Road 40N11) near Adin CA and along the trail between the Lower Campground and Dan Ryan Meadow at Ash Creek, also in the Modoc National Forest near Adin CA.