Magnolia scales overwinter as nymphs (immature instar) on one- or two-year old twigs. The dark grey or brown nymphs are oval, 1 to 2 mm long, with a waxy coating.
In spring, the nymphs become active again, start feeding again and moult.
Female nymphs gradually become larger and covered with a layer of whitish powder. Male nymphs are much smaller (about 35 mm), with flattish bodies that turn translucent white in early summer.
Nymphs reach adulthood in early July (Montréal region). Mature females have oval, smooth and convex bodies. They can reach sizes of up to 12.5 mm. Males metamorphose into winged insects resembling tiny pink or yellow gnats. They mate with females and then die.
Females lay their eggs under their coverings. At this point they are very large and have often lost some of their whitish coat. They take on a pinkish colour before the nymphs emerge.
As the eggs hatch (mid-August to mid-September), the young nymphs leave the mother’s protective covering and move to new feeding sites. This “crawler” stage lasts about 48 hours. The nymphs then attach themselves to twigs where they will overwinter.
Newly hatched nymphs are a tan colour but turn darker once they start feeding. At this point, the young nymphs have no covering as yet. It takes about ten days before they secrete their first protective waxy coating.
There is only one generation of magnolia scales per year.