DALLAS (CBSDFW.COM) – The first round of aerial spraying in Dallas County is now complete. All four planes are back on the ground at Dallas Executive Airport — the last one landed at about 3:00 a.m. Monday morning — after attacking mosquitos with pesticide in the fight against the West Nile virus. The spraying started on Thursday night and was delayed several times over the weekend due to heavy storms in the area.

Of course, that rain also left behind large pools of water which, officials said, could provide breeding grounds for more mosquitos.

Data is coming in about the effectiveness of the aerial spraying, and it shows dwindling numbers among the type of mosquito most likely to carry the West Nile virus. That is exactly what Dallas County Judge Clay Jenkins liked to hear, as he watched the planes take to the skies on Sunday night. “It just gives me a kind of sense of relief to see them take off,” he said. “The faster we get this done, the safer we’re all going to be.”

Clarke Dynamic Aviation is the business handling the aerial spraying. Company spokeswoman Laura McGowan said Monday morning, “We’re very, very happy to report that we covered about a quarter of a million acres last night.”

McGowan also answered questions about the spraying. “It’s a very sophisticated process to use aerial spray for mosquitos. The droplets come out in sizes that are so small — they’re about 30 microns, smaller in diameter than a human hair. So, these are droplets that remain very, very light. They actually float in the air for a great deal of time,” McGowan said. “These are products that are designed to react with a mosquito’s biology.”

Five planes are scheduled to go up again on Monday night, hitting Dallas County with another round of aerial spraying. “Next on the agency is a full round of second-round spraying this evening. We hope to cover about 360,000 acres, every place that has been identified in the spray blocks from Thursday, Friday or Sunday nights will receive a second round of spraying tonight,” McGowan said. “It should go off without a hitch.”

Meanwhile, the cities of Arlington, McKinney and Waxahachie will conduct ground spraying on Monday night.

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