Adelges cooleyi (Adelgidae)

the Cooley spruce gall adelgid

5 pairs of spiracles

Adults:

Adelges cooleyi has a life cycle that typically takes two years to complete, and involves 6 distinct generations, five of which are parthenogenetic females. 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. Non-migratory, 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.

Nymphs:

Light brown when first hatched, black when settled; they are flattened oval in shape and secrete a fringe of white wax.

Damage:

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.

Principal Hosts:

Picea species are the primary hosts; Douglas-fir is the secondary host.

Economic Importance:

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.

See also HForest, Diseases and Insects in British Columbia Forest Seedling Nurseries, and JP17.

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