Seasonal development
and life cycle—Adelgids
Most adelgid species alternate generations between two different conifers. Adelgids commonly form galls
on spruce, which are considered the primary host on which these insects undergo sexual reproduction and
overwinter. Pines are the alternate host for Pineus species, and Adelges species feed on
Douglas fir, fir, hemlock, or larch as their alternate host.Adelgids on their alternate hosts are recognized
by the cottony white or grayish material secreted by colonies of females on the trunk, limbs, cones, twigs,
or needles. Heavily infested trees may seem covered with snow. The adelgids themselves are beneath this
material.
Most adelgids have a complex life history. The conifer species serving as the primary or secondary host
is not known for all adelgids, and some populations apparently don't migrate between hosts. The insects
can look different depending on the host, and each species typically has several different kinds of egg-laying
adults. Most species overwinter as eggs under cottony masses or as early-stage immatures under bark or
bud scales.
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Cooley spruce gall adelgid egg
Cooley
spruce gall adelgid nymphs
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