This species evidently has more than one generation per season; R.J. Gagné (in litt., 9 August 2013) reared adults in July from specimens collected two weeks earlier in Maine, whereas the larvae I collected in August [from Spiraea tomentosa] overwintered before emerging as adults.

[Also includes a rearing record from Spiraea alba]

... induces monothalamous, midrib fold galls and occasionally leaf-margin roll galls on mountain meadowsweet (Spiraea splendens) and steeplebush (S. douglasii) ... These long, swollen galls are usually pink to rose red ... those on the ventral midrib protrude ... Larvae exit through a longitudinal slit and pupate in leaf litter the following spring ...

[photo Plate 477]

Globular midrib swelling

Galls are especially visible from below. This is the species responsible for the damage. Larvae are gregarious. When full grown they leave the gall through a dorsal longitudinal slit.
Hosts: S. betulifolia, S. latifolia, S. salicifolia, S. tomentosa
Distr: New England to Ontario and British Columbia to Oregon