Now that the 17-year cicadas are back and soon to grace this region with their mating songs, the Porter County Purdue Extension Service offers some tips to prevent cicada damage to young trees.

The Periodical cicada (17 year brood XIII) emerge in this part of the country every 17 years. Distributed across the eastern United States, they exist nowhere else in the world. For the past 17 years, they have been underground feeding on tree roots. Upon emerging in late May, they crawl onto vertical plants and other structures, where they molt into adults. They will then mate seven to 10 days later.

The females create slit-like wounds in tree limbs to deposit their eggs. After six weeks, the eggs will hatch into nymphs that will fall to the ground and crawl beneath the soil, where they will feed on tree roots and not emerge again until the year 2024.

The Periodical cicada achieves high population densities, far more than most other cicada species. Their most common population density is in the range of tens to hundreds of thousands per acre, though they can reach densities of as much as 1.5 million per acre.

Cicadas do no bite or sting. And for the most part, they will not devastate crops or gardens, according to Todd Hudson, Purdue Extension Educator.

However, the female cicadas have the potential to damage plants by the wounds they create in which they deposit their eggs. These wounds may weaken or kill a branch, and typically, the branch tips will brown and break off and fall to the ground.

The female cicada prefers to lay its eggs in branches with a diameter of 3/16 to 7/16 inch. They lay eggs on more than 200 species of tree, including oak, hickory and flowering fruit trees. They tend to avoid birch, magnolia, and evergreen.

Larger and otherwise healthy trees should not be significantly damaged. The threat is more substantial to the smaller, younger and recently planted trees whose main stems are less than one-half inch.

These small trees can be protected with nylon netting or cheesecloth during the egg-laying period. The netting should have a mesh of no less than 1/4 inch and should be placed over the trees when the first male songs are heard. The netting should be tied to the trunk beneath the lower branches and can be removed after adult activity has ended. Young twigs that have been damaged by egg laying should be pruned and destroyed within a three-week period after eggs are laid. Doing so will prevent newly emerged nymphs from reaching the ground. After emerging from the ground, cicadas may be consumed by dogs and cats, but they cause no harm to these animals. These pets will occasionally eat so many of the cicadas that they can become constipated or regurgitate.

For more information about cicadas, click the cicada story at www.entm.purdue.edu/entomology

Posted 5/30/2007