LURAY, VA. (CBS19 NEWS) -- Next month, the Shenandoah National Park and the U.S. Forest Service will be spraying for an invasive insect species along Skyline Drive.

However, officials are not sure what days exactly this work will take place because weather conditions can be unpredictable and variable.

At this time, the likely dates are between May 15 and 17 or May 20 and 21, based on historical spraying activities.

The work will target the nonnative species spongy moth caterpillars, which people may more commonly know as gypsy moth caterpillars, between mile markers 39 and 51 of Skyline Drive and in the Skyland and Big Meadows areas.

According to a release, once a date has been established for the work, park officials will notify members of the public through signs, handouts at entrance stations, online and on social media.

Spongy moths first came to this country in the 1860s and the species has been slowly spreading across the country since then, including most of Virginia.

Spongy moth caterpillars cause defoliation, which healthy trees can likely withstand for one or two consecutive years.

But stressed trees are more susceptible to issues associated with defoliation, especially if it affects more than 50 percent of the tree’s leaf cover.

The U.S. Forest Service says crown dieback can occur after extensive spongy moth feeding, and tree mortality can result from repeated bouts of severe defoliation of more than 75 percent of the tree’s leaves.

SNP will be using a naturally occurring bacterium called Bacillus thuringiensis, variation Kurstaki, or Btk, as an aerial pesticide.

This bacterium is widespread in natural ecosystems, and SNP says it is not harmful to people, pets, plants or most beneficial insects.

Btk is sanctioned for use against spongy moths, and the national park will be spraying a total of 3,150 acres from a specialized helicopter between 6:30 a.m. and 12 p.m. on two mornings.

The release says spongy moth numbers have grown over the past two years, causing forest defoliation in large areas of the central part of the park.

It says additional defoliation events would likely cause significant tree mortality, resulting in safety hazards in high visitor-use areas and damage to regional habitats.

The goal is to reduce hazardous tree development and to protect sensitive historic and natural areas, not completely eliminate the moth from the national park.

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