Adelges cooleyi (Adelgidae)
the Cooley spruce gall adelgid
5 pairs of spiracles
||Adelges cooleyi has a life cycle that typically takes two
years to complete, and involves 6 distinct generations, five of which are
Adult female adelgids which migrate between hosts
are a dark red-brown colour, with a heavily sclerotized thorax. Two pairs of wings
are present, and mouthparts are thread-like stylets.
overwintering adelgids are small, globular, and wingless (1.2-1.7mm). Only females
occur at this stage. Each leaf feeding individual is covered by an obvious patch
of white wax wool. Mouthparts consist of thread-like "stylets"
which are used to penetrate into vascular bundles for feeding. Mature adelgids
lay many eggs which are protected under the tuft of white waxy threads. When
the nymphs hatch they move to the buds at the end of branches.
Light brown when first hatched, black when settled; they are flattened oval
in shape and secrete a fringe of white wax.
||The full life cycle of Adelges cooleyi involves two hosts: a
primary host, spruce, and a secondary host, Douglas-fir. It is the damage occurring
to Douglas-fir seedlings that is of concern for this laboratory session. Adelgid attack
on Douglas-fir is restricted entirely to the needles; feeding causes needle
discoloration and distortion, resulting in twisted, chlorotic needles. Severe
attacks on nursery stock can result in a check to growth.
In the primary host, spruce, feeding around the base of the needles in an expanding
bud causes the basal portion of needles to thicken and expand, and the coalescence of these swellings
forms the characteristic "gall" on new growth.
species are the primary hosts; Douglas-fir is the secondary host.
The damage caused by this insect on its primary host is of little importance
under normal forest conditions. However, on nursery stock and ornamental
trees the damage can cause significant deformation of the crown shape. In
seed orchards, gall of cones greatly reduces seed yield.
On its secondary host, severe infestations on poor sites may cause heavy
shedding of foliage. This discoloration and loss of needles can be very damaging
in Christmas tree plantations as well as nursery stock.
References and Links:
EAG: 553-554; FC: 102-106.
For a useful diagram of the life cycle of the Cooley spruce gall adelgid, and other general information, see the Colorado State University Extension Insect Fact Sheet on Cooley Spruce Galls.
Common woolly aphids and adelgids of conifer in B.C.
See also HForest, Diseases and Insects in British Columbia Forest Seedling Nurseries, and JP17.