The periodical cicada female uses her ovipositor to make a slit in small twigs of trees, but will lay eggs in branches up to one-and-one-half inches in diameter. The female then lays her eggs in these slits. The eggs hatch and the nymphs fall to the ground and tunnel down through the soil to feed on sap in a root until they emerge 13 or 17 years later. Although their feeding on the tree’s roots for 13 or 17 years have an impact on the growth of the tree, they do not cause enough damage to justify any control measures. The egg-laying slit made in the twig may cause the twig to dry and break off. This damage, too, is not harmful enough on an established tree to justify trying to control these insects. However, small transplanted trees, particularly fruit trees, commonly have a trunk diameter small enough that egg slits made in the trunk, may result in the tree snapping off.
Insecticide applications kill huge numbers of visiting cicadas, but analysis of egg-slit trunk damage shows little difference between treated and untreated research plots. The only way to protect small trees from serious damage in a heavy emergence area is to protect the trunk with screening or other material. This is expensive in materials and labor. It is much better to delay small-tree planting for a year or install larger stock, preferably those with a trunk diameter of at least 2½ inches.
Some thought about periodical cicadas and their needs can also help. Realize that these insects require a steady supply of sap-supplying tree and shrub roots for 17 years. Housing developments that have had all trees and shrubs removed prior to building will have few cicadas because the nymphs died when the trees were removed. Similarly, housing developments in areas that were originally farm fields or prairie will have few cicadas due to the original lack of trees. The practice of bulldozing all trees off of a housing development site has been common only since the 1960s, so older housing developments tend to have large numbers of cicadas.
The periodical cicada flies only a short distance, apparently less than one-half mile, from where it emerged from the soil. Therefore it expands its territory very slowly considering its long life cycle. We are not used to thinking of insect life cycles longer than one year. Only nine generations of 17-year periodical cicadas ago, Abraham Lincoln was practicing law in Illinois prior to the Civil War. During the intervening time, periodical cicadas have probably spread only about 5 miles. Consider, for a moment, what most of Illinois was like before the 1900s. Large areas of prairie had periodic prairie fires that killed many trees. With prevailing west winds, large prairie fires would have moved east with the wind. Rivers that run roughly north to south, such as the Fox, Des Plaines, Illinois, Rock, and Mississippi Rivers would have functioned as firebreaks. Trees would have survived much longer on the east sides of these rivers, and so would the periodical cicadas. As a result, we see higher populations of periodical cicadas in East Peoria than in Peoria, Rockford east of the Rock River, and similarly along other rivers.