When raking leaves, putting away patio furniture and dealing with other outdoor chores that should be done before winter sets in, an observant individual may notice small, fuzzy, bluish-white insects slowly drifting through the air.
Upon close examination, these gnat-like bugs have an abdomen covered with a mass of tiny, curly, white fibers and a thorax that is a light iridescent blue-green, especially near the base of their transparent wings. These tomato seed-sized invertebrates are known as woolly aphids, and although they are active from mid-spring through October, it is only after the leaves have fallen and they take to the air that they become marginally visible to anyone that spends time outside.
The woolly alder aphid is probably the most abundant member of this group in the Adirondacks. As its name implies, this sucking insect depends on alder, an exceptionally common shrub in wetlands throughout the Park, for its food during the summer and the early days of autumn. Like any aphid, this bug gets its nourishment by piercing the outer layers of tissue in certain spots, and then tapping into the flow of sap that exists beneath the surface. Because sap contains sugars formed during photosynthesis, an aphid primarily acquires these sweet-tasting carbohydrates rather than a variety of nutrients as it siphons the sap from a plant.
However, in order for an aphid to develop cellular tissue of its own and form the many embryos that an adult is programmed to produce during the course of a season, protein is needed. Enough of these nitrogen-based compounds can be collected by an aphid if it processes a high enough volume of sap. Since an aphid is unable to oxidize all of the sugars that are extracted from the sap, and because its body does not store excess carbohydrates in the form of fat, the unused sugars are eliminated from its body in droplets known as “honeydew”. (Duplicating the aphid’s ability to discard excess sugar from the body rather than transforming it into fat in a human would be the ultimate dream of any dietary scientist.)
Many types of ants have evolved the ability to locate colonies of aphids for this sugary residue. Biologists have observed ants vigorously protecting clusters of aphids from larger insect predators, as ants rely on the residue of aphids as an important food source.
Unlike most insects, and other forms of life, aphids reproduce mainly by asexual means. Once a female aphid finds a spot on a plant where she is able to extract adequate amounts of sap, she begins to bear offspring without first breeding with a male. In this way, the aphids produced are genetically identical to the sole parent, or are clones of their mother.
Additionally, during this stage of its life, the woolly alder aphid does not lay eggs; rather the female bears live nymphs that tap into the same location on the alder and quickly develop into adults. Within a few weeks, the offspring are reproducing nymphs of their own and add more tiny clones to the expanding colony.
During the final days of summer, the amount of sap in the shrub begins to dwindle, triggering a change in the reproductive behavior of the aphids. Males are formed during this period of time, and wings develop on the body of the maturing adults which provide these normally flightless bugs with the ability to abandon their colony.
After mating, the female aphid attempts to travel to a red or silver maple in which to deposit an egg. It is beneath a crack or crevice in the bark of this tree that the egg passes the long winter. When spring arrives and as soon as the sap begins to flow, the egg hatches and a nymph emerges to take advantage of the maple’s rich source of nutrients.
After another generation of winged adults is produced, these tiny bugs take to the air once again and migrate back to a wetland in their search for an alder. Since the rate of sap flow and nutrient composition differs in these two woody plants during the course of the year, this aphid changes its host in order to better serve its needs.
The aphids form a complex group of sucking insects that rarely do any serious harm to trees or shrubs like alder because of their large size. Small house plants are another story, as these are attacked by other species of aphids that can inflict more pronounced damage to a smaller host.
The woolly alder aphid is just one of many species, however it is the one that is likely to be encountered at this time of year while outdoors here in the Adirondacks.