HARRIS COUNTY, Texas – County health officials say the public should not fear the spray being used to control the mosquito population in Harris County.

Aerial spraying to combat the mosquitoes is scheduled to begin in Harris County on Thursday evening. The operation may take more than a day.

Harris County Public Health says the rain left behind created large areas where mosquitoes can lay their eggs. The U.S. Air Force Reserve’s 910th Airlift Wing will fly a modified C-130 cargo plane to conduct aerial sprays.

The plan is to spray 600,000 acres, mostly outside of the City of Houston limits.

Related: View spray areas & ZIP codes shaded in yellow (PDF)

Some residents living in a Pearland neighborhood rushed outside at around 9 p.m. Wednesday night when they heard the loud sounds passing over their homes.

State health officials say the planes have already covered nearly 2.5 million acres of Texas land since Hurricane Harvey passed.

The planes are spraying a mixture containing the mosquito-killing chemical commonly known as naled. They say it kills the mosquitos in the air on contact.

According to Dr. Umair A. Shah, executive director of Harris County Public Health (HCPH), “The goal is to reduce the effects mosquitoes are having on recovery efforts and the possibility of a future increase in mosquito-borne disease.”

“The insecticide, Dibrom (EPA-approved), is routinely used for aerial spray operations to combat mosquito-borne disease and will be used during the spray operation in Harris County. Dibrom is considered safe for the environment and is applied by licensed applicators, according to the label instructions,” the county stated in a press release.

Some residents of southeast Houston, where the spraying will begin in Harris County, told KHOU 11 News Thursday they are still concerned.

“I think that’s going to be hazardous, harmful,” one neighbor said near the Almeda Mall. “Of course they’re doing it to kill mosquitos but hazardous and harmful, that’s how I feel about it.”

For residents concerned about exposure, HCPH recommends they stay indoors during the evening aerial application in the treated areas, as a precaution.

As an extra precaution, beekeepers may wish to cover their colonies to prevent bees from exiting during treatment.

Remember residents can help control mosquitoes by emptying standing water around their homes.

The spraying will continue on Friday in portions of Harris County and then move north into Montgomery County.

Related: Officials step up mosquito spraying in Houston-area counties