In previous episodes, we met interesting sap-suckers like the hemlock woolly adelgid and flattid planthoppers, members of the Hemiptera that produce copious amounts of flocculent wax as a means of protection from hungry predators and stinging parasites. This week we meet another member of the sucking insect clan that makes its presence known by producing gobs of fluffy white wax. Woolly alder aphids live a complex life (yes, insects do have complex lives) in which they alternate between a generation reproducing asexually (no guys, just gals), and one reproducing sexually with both males and females adding to the diversity of the gene pool. On a sunny late autumn day, I spied several clusters of woolly alder aphids lining the branches of small alders along the banks of Lake Kittamquandi in Columbia, Maryland. These large colonies were members of the asexual generation of woolly alder aphids. These waxy ladies persist for several generations on the bark of alders and are thought to survive winter’s onslaught in situ. Earlier in the fall season some females produced sons and daughters, part of the sexual generation, which took flight and migrated to nearby maple trees. There they mated and females produced a single egg each, deposited on the tree’s bark. With all of her eggs in one basket so to speak, these propagules, if they survive, hatch in spring and initiate a new asexual generation of aphids that feed on the leaves of maples. This generation of maple-feeders goes by the name of maple blight aphids. Their numbers are often prodigious and their white fluffy wax sometimes cloaks the entire surface of a leaf.
Fluffy wax cloaks the bodies of these independent ladies that reproduce without any assistance from male aphids. Tiny nymphs wander about seeking a place to settle down to suck sap from alder stems.
From this early season asexual generation on maple, migrants are produced that transit to nearby alders and initiate the asexual alder feeding generation. Migrating woolly alder aphids look like tiny balls of flying cotton as they wing their way in search of alders to colonize. I warned you that the life of these aphids is complex. The good news about these waxy herbivores is that their feeding is believed to cause little or no significant damage to the trees and shrubs on which they feed. Like aphids and scale insects we met in previous episodes, sweet honeydew excreted by woolly aphids is a substrate for a nonpathogenic fungus called sooty mold that may blacken leaves and bark beneath colonies of aphids. Woolly alder aphids provide a feast for many types of predators, including several species of the lady beetles and maniacal lacewing larvae. If your late autumn walks take you to lakesides or stream banks populated by alders, keep an eye open for these curious waxy ladies.
The wonderful reference "Insects that Feed on Trees and Shrubs", by Warren Johnson and Howard Lyon, was used to prepare this episode.