Hurricanes Irma and Harvey blew away many mosquitoes, but standing water left behind provides ideal breeding grounds for these infectious pests.

Hurricanes Irma and Harvey left behind devastation in large parts of the United States.

However, the strong winds also swept away much of the mosquito population in the affected areas in Texas, Florida, and elsewhere.

That relief was welcome, but it may be short-lived.

That’s because it can take only a couple weeks before mosquito populations increase again.

An official with the Sarasota County Mosquito Control District told the Sarasota Herald-Tribune he expects mosquito numbers to start to spike by Monday.

And it’s not just the sheer number of these pests that increases the risk of mosquito-borne diseases such as the West Nile and Zika viruses.

“What we saw in New Orleans post-Katrina were a couple of things — we think mosquito production was an issue, and human exposure was an issue,” Dawn Wesson, PhD, an associate professor at the Tulane University School of Public Health and Tropical Medicine, told Healthline.

Standing water left behind after the hurricanes is a prime spot for mosquitoes to lay their eggs and hatch more winged pests.

Pots, buckets, and wheelbarrows are all potential sources of new mosquitoes. But so is the water that collects in bromeliads and other small containers.

In New Orleans, after hurricane Katrina in 2005, flooded swimming pools were a big problem.

“It was a while before those swimming pools were able to be brought back online, cleaned up, or drained,” said Wesson. “So those became major mosquito production sites.”

She said this could be a problem in areas hit by hurricanes Irma and Harvey, “especially in Florida, where there are a lot of in-ground swimming pools.”

The floodwaters themselves were not as much of a problem post-Katrina.

“We didn’t really find a lot of mosquito breeding in the floodwaters themselves,” said Wesson. “We speculate that this was because of gasoline residue and other chemical residue in the waters that just really didn’t make them conducive to mosquito breeding.”

Property damage and ongoing power outages will also increase the amount of mosquito-to-person contact.

“We think a big contributing issue to increased West Nile infections in the area affected by Hurricane Katrina, both in Louisiana and Mississippi, was human exposure,” said Wesson.

With damage to houses, people may be sleeping outside or in exposed parts of the house.

And lack of power may mean they’ll need to keep the windows and doors open in the heat.

A big concern after these hurricanes are diseases transmitted by mosquitoes.

Texas is among the states with the highest number of West Nile virus and Zika cases this year. Texas health officials have reported 71 human cases of West Nile virus as of this week, along with three deaths.

The state also had 27 cases of Zika. This includes one locally transmitted infection in late July.

The person who tested positive had not traveled outside the state.

This makes a mosquito bite in Texas the “probable source” of infection, according to Texas Health and Human Services.

So far this year, Florida has had no reported cases of West Nile virus in people, and 50 reported cases of Zika virus disease, according to the Centers for Disease Control and Prevention (CDC). None of the Zika cases were acquired locally.

Many areas in the Southeast already had mosquito control programs before the hurricanes, but these may get a boost post-hurricane wherever possible.

“They may have set up alliances with other mosquito control programs outside of what was expected to be areas of impact from the hurricane,” said Wesson, “to potentially get them in there helping with surveillance, or aerial or truck-mounted spraying if that’s deemed necessary.”

In the county where Houston is located, officials are taking preemptive measures to head off a mosquito explosion.

The U.S. Air Force Reserve will spray insecticide over roughly 600,000 acres using modified C-130 military cargo planes.

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

The county said the insecticide, naled, is approved by the Environmental Protection Agency (EPA) and safe for the environment. However, officials recommend that people and their pets stay inside during the aerial spraying.

Beekeepers may also want to cover their colonies during that time to keep their bees safe from exposure.

People can also help reduce mosquito populations by draining or covering standing pools of water found in buckets, flower pots, gutters, tires, and even outdoor dog bowls.

They can also protect themselves by wearing long sleeves and pants, and using insect repellents.

This is especially important for paramedics, firefighters, and other responders who are often out in the open for hours at a stretch.

“They should remember to wear repellant and remember to protect themselves,” said Wesson, “because even though West Nile may not always be severe, it can also be quite severe and it can kill you.”