The 17-year cycle of the cicadas has come full circle, which means growers in several Eastern states should be on alert this spring.
However, an expert in Penn State’s College of Agricultural Sciences says it’s not a cause for immediate alarm.
“These insects are harmless to people, but they can cause some damage to shade trees, fruit trees, and high-value woody ornamental plants,” says Gregory Hoover, Senior Extension Associate in entomology at Penn State.
The periodical cicada is native to North America and exists nowhere else in the world. There are six species of periodical cicada, three with a 17-year cycle and three with a 13-year cycle.
The cicadas surfacing this year are members of Brood II, which was last seen in 1996. States where cicadas are likely to emerge include Pennsylvania, Ohio, Connecticut, New Jersey, New York, Maryland, Virginia, and North Carolina.
In some affected areas where the ground is damp, Hoover notes, observant homeowners already may have noticed that periodical cicada nymphs have built small earthen turrets over their exit holes to protect their escape routes from too much moisture.
Any damage caused by periodical cicadas occurs during egg-laying. Using the blades of a saw-like device on her abdomen, a female will cut several small pockets in the bark of a twig before depositing 400 to 600 eggs.
This process can cause the foliage on small twigs to wilt and may provide an opening for a plant disease. Adults live only a few weeks, but the twig injury they cause may be apparent for several years.
Protection methods include covering the crown of valuable trees with a fine mesh, being sure to tie off the covering around the base of the tree to prevent adult females from accessing the crown of the tree. Growers may elect to delay the planting of trees until fall since adult periodical cicadas are gone by early July.
Although adult cicadas are difficult to control, Hoover suggests that nursery owners or others with trees at risk may want to apply registered insecticides around the time mating starts — about 10 days after they first hear the males singing. If a registered insecticide is used, label instructions should be read and followed carefully.
Hoover emphasizes that periodical cicadas do not damage field crops, and residents who live where land has been cleared of trees may not see them.
“Members of Brood II may not be as abundant as they were in the past or as other broods — such as Brood X in 2004 and Brood XIV in 2008 — in part because of development and habitat loss,” he says.
Adult periodical cicadas are about 1½ inches long with reddish eyes and orange wing veins. They are smaller than their cousins, the annual or dog-day cicadas usually seen and heard in the heat of late summer.
Cicada nymphs spend 17 years from 2 to 24 inches underground, sucking nutrients from xylem cells in plant roots. In late April and May, they burrow to within an inch of the soil surface, where they await an undetermined signal for emergence.
“Soil temperatures reaching 64°F and a light precipitation event seem to be prerequisites for cicadas to emerge,” Hoover says.
When the time is right, usually in mid to late May, the nymphs exit the soil through half-inch holes and climb a foot or more up trees or other objects. Within an hour, they shed their nymphal skins and become adults.
Adult cicadas are clumsy flyers, often colliding with objects in flight. Males begin their constant singing shortly after they emerge, but the females are mostly silent. When heard from a distance, the cicadas’ chorus is a whirring monotone.
On rare occasions when an adult eats, it sucks fluid from small twigs but does not feed on leaves. Ten days following emergence, mating takes place.
Adults live up to four weeks above ground. Six to seven weeks after the eggs are laid, nymphs hatch and drop to the ground. There, they enter the soil, not to see the light of day for 17 years.
A fact sheet on periodical cicadas can be found on the Penn State Department of Entomology website.