DALLAS — The last time Dallas used aerial spraying to curb the mosquito population, Texas’ Lyndon Johnson was in the White House, Mission Control in Houston was launching Gemini missions and encephalitis was blamed for more than a dozen deaths.

But for the first time in more than 45 years, Dallas County has launched an aerial assault on the flying pests. Aircraft took off at 10 p.m. Thursday to spray insecticide over the county’s northeastern quadrant to combat the nation’s worst outbreak of West Nile virus. That outbreak has killed 10 people and caused at least 230 others to fall ill.

“I cannot have any more deaths on my conscience because we did not take action,” Dallas Mayor Mike Rawlings said

Although commonplace in other major cities, the efforts are provoking a debate in the Dallas area between health officials trying to quell disease risk and people concerned about insecticidal mist drifting down from above.

Nearly half of all West Nile cases in the United States so far this year are in Texas, according to the Centers for Disease Control and Prevention. If the trend continues, 2012 will be the worst West Nile year in state history.