Periodical cicadas, Magicicada spp., emerge in specific locations once every 17 years in the northern part of their range and once every 13 years in the southern part. Every year periodical cicadas emerge somewhere in the eastern United States. The different groups that emerge each year in different locations are called “broods.”
The group that emerged in 2004 is known as Brood X (Brood 10) and is the largest of the 17-year cicadas. The last time Brood X emerged was in 1987 and occurred in parts of 15 states from New York to Georgia to Illinois and Michigan. Media coverage of the emergence of Brood X began as early as January because of the massive numbers of insects expected to appear on the scene and the negative response that these insects were expected to stimulate in people who live in areas where the emergence occurs.
Periodical cicadas belong to the insect order Homoptera, so they are sucking insects. When viewed head-on, or from the side, the adults vaguely resemble giant aphids. Although cicada adults have sucking mouthparts, they do very little feeding, and their feeding damage is considered insignificant.
The female cicadas produce the most dramatic damage when they lay eggs. They deposit eggs by jamming their long, sturdy ovipositors through the bark and into the wood of twigs and small branches. They prefer oviposition material with a diameter of 1/4 to 1/2 inch. The females usually inch forward as they lay eggs, producing longitudinal slits.
Multiple oviposition slits may kill the twigs and small branches, producing a symptom called “flagging.” On a large tree, the damage is of minimal consequence to the overall health of the tree. However, damage on small trees may have a significant impact on tree health when a high percentage of branches are affected.
The literature indicates that females may lay eggs on more than 270 species of plants, including most of the deciduous tree species found in Ohio. Some of the more unusual hosts include Rose of Sharon, rose, raspberry, grape, black-eyed Susan, hollies, spirea, rhododendron, viburnum, junipers, and arborvitae. Egg laying has even been observed on annuals and herbaceous perennials.
However, lists of possible oviposition hosts should always be viewed “through the lens of common sense.” The nymphs that hatch from the eggs cannot move far from the oviposition host selected by the females, and the nymphs need to feed for 17 years. Rarely are cicadas a significant threat to herbaceous plants in home gardens and landscapes.
Periodical cicadas are truly a fascinating biological phenomenon. After spending 13 to 17 years feeding, growing, and developing under the soil, they emerge from the soil somewhat synchronously to become adults. Most nymphs in a particular area crawl out of the soil within a few nights of one another.
In Ohio, in 2004, Brood X was expected to emerge in scattered locations throughout much of the western half of the state. Some locations had huge populations while others had little or no populations, which, though a relief to most, was disappointing to entomologists living in those areas. Distribution maps of where and when the different broods of periodical cicadas emerge can be found on Ohio State University Extension Fact Sheet HYG-2137-99, Periodical and Dog-Day Cicadas, and on several sites on the World Wide Web — e.g., http://bugs.osu.edu/~bugdoc/PerioCicada/.
Periodical cicadas cause a lot of excitement when they appear for several reasons. First, in some areas, hundreds of thousands of these 1-1/2”-long insects are found per acre, sitting on everything and flying through the air. For people who don’t like insects, massive numbers of insects surrounding them can be quite disturbing.
Second, the song the adult males produce is very loud and, multiplied by thousands, the noise can be deafening. Often the males synchronize their singing and can be heard more than one-half mile away.
Third, although the adults do not feed excessively, females can damage trees and shrubs by depositing eggs in slits they produce in twigs and stems. The splintering of the wood and bark of the small twigs and stems may result in twig dieback. Fourth, some pet owners discover their dogs and cats eating the emerging cicada nymphs.
Chorusing is used by male cicadas to attract the females. The sound is produced by very obvious white-colored structures called tymbals located beneath the hind wings on each side of the top of the abdomen. Males congregate en masse in trees and react to one another with their songs rising and falling in unison. Females also produce sounds, but they use their wings. In response to the male’s love song, the females vibrate their wings. This “wing flick” behavior produces a soft, rustling broad-frequency sound, or a sharp snapping noise.
Massive brood emergence is believed to overcompensate for the feeding of predators, which are mostly birds. This ensures that enough survivors will be left behind to reproduce. Male cicadas are capable of making a loud buzzing noise and squawk when disturbed. The males often synchronize their buzzing in trees, producing a deafening noise. It is believed that such droning and squawking is effective in deterring predators.
The availability of large numbers of insects in a concentrated area can cause changes in behaviors of many different animals, resulting in unusual and sometimes mysterious looking symptoms. During a plant diagnostic event at Spring Grove Cemetery and Arboretum in Cincinnati, participants observed hundreds of round or oval-shaped holes about 1” to 1.5” in diameter and 3” deep throughout a rain-saturated area under some trees. The size of the holes and lack of soil mounded around them indicated that they were not periodical cicada emergence holes, although there were many of those in the area.
The holes were too neat and small to be the work of raccoons digging for cicada nymphs or other subterranean insects. Further observation revealed the causative agent of the holes when a trio of mallard ducks waddled under the trees. The mallards, far from a pond or other water, began drilling their bills into the soil with a twisting motion until their eyeballs were barely visible above the soil line. They were enjoying the once-in-a-lifetime (for a duck) opportunity to fatten up on cicada nymphs and, in the process, were leaving the tell-tale holes as evidence of their good fortune.
Mallards are not alone in taking advantage of the plentiful supply of protein in the form of insects. Numerous birds, snakes, moles, and other mammals will stuff themselves with the easy prey. Unfortunately, family pets — dogs and cats — will also consume excessive numbers of the cicadas, with resultant regurgitation after a short period of time.
Increased public awareness of the Brood X emergence escalated concerns as to how to prevent severe damage to tender plant materials. The management tactic adopted by many homeowners was to wrap critical plants in various coverings in an attempt to prevent female cicadas from ovipositing in twigs and branches. Many misuses or misunderstandings as to how to use tree canopy coverings to prevent oviposition were observed in different areas of the state.
Some examples of misuse included trees wrapped two to four weeks earlier than necessary; trees wrapped too tightly, with cloth spiraling around compressed branches and held firm from top to bottom by rope bindings, producing what appeared to be “tree-mummies;” and some tree canopy coverings where cloth was secured only to the trunk and basal branches of the tree. With this latter approach, the upper canopy was left uncovered and susceptible to oviposition damage.
Covering small, newly planted trees with light-weight cloth (e.g., cheese-cloth), netting (openings 1/4” or less in size), or other appropriate material will prevent cicada oviposition injury. This is a recommended practice in areas where high cicada populations portend significant damage to small trees.
However, this method of reducing cicada damage is not without risk to the “protected” trees. Here are some common-sense points to consider:
Ohio State University Extension personnel kept a close watch on the development of the Brood X cicadas from the start of their late springtime activities until well after the singing of the males had ceased. Selected observations made through the cicada event are presented here:
Brood X emergence began in early May (May 4 to 11, 2004), and the adult activity extended into late June to early July (June 29 to July 8, 2004), although their impacts will be felt for several years to come. During the cicada emergence, and subsequent adult activity, Ohioans living in heavily infested areas met the onslaught with a range of reactions, from genuine curiosity and amazement, to taciturn acceptance, to mild panic. Their sentiments are epitomized by a few selected farewells — “goodbye garish gadflies,” “adios transient troubadours,” and “don’t let the door slam on your ovipositor on the way out.”
Curtis E. Young, Ohio State University Extension, Allen County; Joseph F. Boggs, Ohio State University Extension, Hamilton County, OSU Extension Center at Piketon; and David J. Shetlar, Ohio State University Extension, Ohio Agriculture Research and Development Center, Entomology.