Alder aphid (Pterocallis alni)
Hop aphid (Phorodon humuli)
Woolly aphid (Prociphilus spp.)
Pest description and damage Alder aphids are pale yellow with dark bands on light-colored antennae. Hop aphids are pale yellow-green with coalescing stripes that may form patches. Aphids may nearly cover the undersides of leaves. Feeding by the woolly aphids cause leaves to fold downward over the blue-black aphids found covered by a woolly waxy material. Each species has a portion of adults that develop wings to disperse to alternate seasonal hosts, although the alder aphid does not alternate hosts. Deposit of honeydew and sooty mold beneath host plant are the primary pest concerns.
Biology and life history The hop aphid is one of the aphids common on plum. They overwinter in the egg stage on plum, alder and other trees. In spring, they migrate to hops. The winged form of the woolly aphid (small orange females and blue-black males) migrates from alder to maple where they mate and lay eggs on the bark of maple. Simultaneously, a small wingless form crawls down the alder trunk to overwinter under leaf litter at the base of the tree. They crawl back up in spring or fly back to the alder from maple.
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