Cooley spruce gall adelgid
July 30, 2015
This insect can produce continuous generations on either Colorado spruce or Douglas-fir but normally spends a portion of its two-year life cycle on each host.
Overwintering females on spruce lay eggs near developing buds. Nymphs hatch as bud caps split. Nymphs feed at the base of developing buds in spring producing cone-like galls on the tips of blue spruce branches. Galls open in mid-summer. Emerging adelgids either continue to live on spruce or fly to Douglas-fir to lay eggs. On Douglas-fir they may continue to live or produce a generation that flies back to spruce to produce the gall-forming stage. On Douglas-fir, feeding on needles by nymphs produces yellow spots and curled needles but no galls.
Left: Opened Cooley galls on Colorado spruce. Right: Adelgids on Douglas-fir.
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