Several species of aphids colonize blueberry bushes. The most damaging species transmit viruses that cause poor plant growth. Blueberry aphid (Illinoia pepperi) is the vector of blueberry shoestring virus and blueberry scorch, which is also transmitted by Ericaphis species aphids. (See the disease section for symptoms of these viral diseases.)

Aphid colony on underside of leaf.
Jerry A. Payne, USDA ARS

Aphids overwinter as tiny eggs on blueberry bushes. In spring, young aphids hatch and colonize new leaf growth, living on the undersides of leaves. Populations grow during the summer and can cause sooty mold on fruit if populations are very high. Parasitic wasps and other natural enemies feed on aphids, suppressing their abundance. Scout for aphids on the undersides of leaves, focusing on young shoots at the bases of bushes.

Blueberry Aphid and Blueberry Shoestring Virus Fact Sheet (pdf)