Aphids make their move
“I have never seen so many or different kinds of aphids,” exclaimed Cindy Deffe, environmental sciences instructor at Spokane Community College. On a recent walk on the SCC campus with her horticulture students, they found aphids everywhere, even in her classroom where she has a number of live weed plants set out for study.
“I have to keep washing them off the plants,” she said with a chuckle.
For their size and seemingly simple appearance, aphids are very complex critters. They are small (1/16- to 1/8-inch long) insects that range in color from green to brown, purple, red and black. Most are soft-bodied covered in an exoskeleton while others protect themselves with a waxy, cottony covering. The tell-tale identification marks of aphids are long thin legs, sucking mouth parts, long antenna, a pear-shaped body and a pair of tiny tubes that project from the bug’s posterior. There are literally dozens of different varieties of aphids and most attach themselves to specific plants: rose aphid to roses, cherry aphid to cherry, green peach aphid to peach, Norway maple aphid to maples. The list is endless.
Aphids are masters of reproduction. They over-winter as eggs or adult “stem mothers” on the trunks, branches and roots of host plants. Some aphids stay on a single plant group. Others alternate between different types of plants. The over-wintering eggs hatch as females that can produce live young in less than 10 days. They move to the underside of the leaves where they tap directly into a plant vein and begin sucking on plant sap. Talk about sugar junkies mainlining their fix.
As the colony grows, winged aphids are produced and these fly to a new plant where they begin a new cycle. That means multiple generations are produced over a season. At the end of the season, they change their reproduction to produce eggs which are laid on a variety of plants to over-winter yet again.
Are you totally confused yet? Don’t worry. According to Deffe, because of the complexity and variability of aphid life cycles, scientists are just beginning to understand the details of the cycles and reproduction. Some day, she says, we may be able to use the research to find better environmentally friendly methods to control them.
Aphids’ damage to plants is more of an annoyance and a nuisance to humans who use or enjoy the plants, than to the plants themselves. Even when infestations are heavy and a lot of foliage is distorted, aphids are rarely the cause of a plant’s death.
The main problem with aphids is the sweet, sticky honeydew they excrete, which then drips onto foliage and anything under the plant or tree. The results are sticky, shiny leaves, tiny drops on cars, lawn furniture and virtually anything parked under the offending plant.
To compound the problem, the honeydew attracts ants that feed on the sugar-rich liquid. Ants will actually care and tend the aphids to keep them producing. They will fight off other insects including predators looking for the aphids. If you have ants running up and down plants, look under the leaves for aphids.
Other signs that aphids are present are twisted and distorted foliage and flowers caused by the aphids’ feeding. Another is the presence of a sooty black mold that grows in the sugary honeydew.