Description

Prociphilus tessellatus, the woolly alder aphid or maple blight aphid, often looks more like a small ball of cotton than an insect because it is covered in white, woollike wax secretions. Adults are 2 mm to 3 mm in length. Nymphs and adults are easily identified by the long white waxy filaments produced from glands in the abdomen which protrude from the body in a dense clump. Woolly aphids congregate in large groups, forming fluffy white patches on their host trees that may be many centimeters in length. Removal of the waxy filaments reveals a plump, oval, gray aphid, with a pair of short, stubby cornicles (defensive gland openings) at the end of the abdomen. Like all Hemiptera, this species has piercing sucking mouthparts. However, sexually reproducing forms have reduced or nonfunctional mouthparts and do not feed.

Minute eggs are deposited on the bark of host plants. Immatures resemble small versions of adults. Waxy filaments are produced soon after emergence but are lost during each molt and replenished afterward.

Woolly alder aphids are a member of the aphid subfamily Eriosomatinae (woolly aphids and gall forming aphids), which is placed in a separate family Eriosomatidae in older literature. In Louisiana, the beech blight aphid (Grylloprociphilus imbricator) is similar in external appearance, but feeds on beech trees (Fagus). In contrast, woolly alder aphids are restricted to feeding on alders (Alnus) and maples (Acer). Other woolly aphids known from the southern region, and likely Louisiana, include woolly apple aphid (Eriosoma lanigerum) and woolly hawthorn aphid (Eriosoma crateagi). All require microscopic examination to positively identify, but host plant is a good starting point.

Life Cycle

All aphids are hemimetabolous, which means that they undergo incomplete metamorphosis lacking larval and pupal stages. After hatching, immatures (nymphs) go through several growth stages (instars) before reaching adulthood. The aphid life cycle is more complex than that of most other insects because aphids are capable of reproducing without a mate (parthenogenesis). This type of asexual, clonal reproduction allows aphid populations to grow extremely quickly, with many generations per year.

Woolly alder aphids overwinter as eggs on the bark of silver maple (Acer saccharinum). Female stem mother aphids hatch from these eggs during early spring and feed on sap from the midveins of maple leaves. The stem mother, also called a fundatrix, gives birth without mating to many nymphs known as viviparous females. These females continue reproducing asexually through the spring and summer to build up large aggregations of woolly alder aphids which are visible as fluffy white tufts. Males are produced randomly via parthenogenesis and are characterized by the loss of one X chromosome. Later in the summer, winged forms are produced and migrate to the woolly alder aphid’s second host, alder trees (Alnus spp.). More generations of aphids feed and reproduce on alders, eventually producing clumps of aphids bearing their dense waxy filaments. The wax is produced by glands in the abdomen and functions to deter predators.

During fall, winged, sexually reproducing aphids fly back to maple trees. Mating occurs, and females lay eggs on tree trunks. These eggs remain until nymphs hatch the following spring.

Ecological Significance and Pest Status

Woolly alder aphids play a limited but noticeable role in forest and landscape ecosystems through their feeding activity on host trees. By extracting plant sap from phloem tissue, aphids can influence plant vigor. They also produce honeydew, a byproduct of feeding. Honeydew contains a high concentration of sugars that attract flies, wasps and bees. Several ant species protect aphids from predators and competitors in exchange for honeydew. Aphids allow the ants to gather honeydew directly from their bodies. These interactions represent a classical symbiotic relationship. Research has demonstrated that aphids tended by ants produce more honeydew than those that are not.

Woolly alder aphids are found in eastern United States and southeastern Canada. In Louisiana, potential host plants may include hazel alder and smooth alder. Silver maple, the preferred host for woolly alder aphid reproduction and overwintering, is less common in Louisiana than other maple species like red maple, southern sugar maple, box elder and Drummond’s maple. Woolly alder aphids are not known to vector viruses like other aphid pest species. The major concern, and typically the most common, is a complex of fungi called sooty molds, characterized by dark, fuzzy spots on leaves and branches. These mold coatings do not harm the plant but are unsightly and may be an indication of a large woolly aphid infestation nearby.

Control

Woolly alder aphids are generally not considered serious pests. Heavy infestations may result in twisted curled leaves, chlorotic growth, and honey dew may accumulate on vehicles parked under infested trees. Using a high-pressure water spray will physically and forcefully remove the aphids, as well as honeydew or sooty mold.

In most cases, natural enemies eventually reduce population sizes and minimize direct damage to trees. Insects that prey on woolly aphids include various species of lady beetles (family Coccinellidae), lacewings (family Chrysopidae), hoverfly larvae (family Syrphidae) and tiny parasitic wasps (order Hymenoptera). Larvae of the harvester butterfly, (family Lycaenidae: Feniseca tarquinius) are unusual predators that specialize on woolly aphids. The plump gray to black larvae can occasionally be found embedded within clusters of aphids on branches. The harvester is uncommon in Louisiana, but a few scattered records are represented by specimens in the Louisiana State Arthropod Museum and online sources (e.g., iNaturalist).