SOUTH DAKOTA DEPARTMENT OF HEALTH
FOR RELEASE: October 6, 2003
CONTACT: Kevin Forsch
605-773-3361

Aerial spraying project kills 90% of adult mosquitoes in target communities

    PIERRE – Ninety to 100 percent of adult mosquitoes in the target communities were killed in South Dakota’s September aerial spraying operation, the Department of Health reported today. From September 9-15, Clarke Mosquito Control sprayed 110,000 acres in Aberdeen, Belle Fourche, Britton, Eagle Butte, Ft. Pierre, Hot Springs, Mitchell, Onida, Pierre, Rapid City, Redfield, Sioux Falls, Spearfish, Sturgis, Vermillion and Wagner, the communities hardest hit by West Nile virus. 

     During the spray operation in Sioux Falls, Clarke placed caged mosquitoes at key locations where they would be exposed to the spray. Within one hour of spraying, the knockdown rate ranged from a low of 90% at one cage to 100% at another. Within 24 hours, the mortality rate at all cages was 100%. In contrast, a control group of mosquitoes not exposed to the spray had a four percent mortality rate in the 24-hour period.

    “Sioux Falls was the largest area we sprayed. The methods, the calibration, the chemical concentrations used were exactly the same as in the other 15 communities so the results there are a good indication of the program statewide,” said Kevin Forsch, Health Systems Division Director for the Department of Health.

     Anecdotal reports from citizens and officials in the communities sprayed also indicated a significant decrease in the number of mosquitoes following the operation, said Forsch. 

     He described the aerial spraying as a final and extraordinary step in the state’s response to the disease. The state had previously provided mosquito control training to municipalities in the state and a comprehensive mosquito control resource guide. A state surveillance system provided free laboratory testing of bird, mosquito and human samples to track the spread of the disease. As initial detections were made in a county, the Department of Health notified local officials and encouraged mosquito control measures. As the outbreak reached epidemic proportions, the state sought and received $300,000 in federal funds to support the targeted spraying of affected communities.

     State Epidemiologist Lon Kightlinger warned that those areas of the state that have not yet experienced a hard frost are still at risk for West Nile and people should continue taking precautions. He also encouraged communities to begin planning now for next year’s reappearance of West Nile virus (WNV). “Now that the WNV season is winding down, we must plan ahead for next year’s mosquito control. Each community must take charge of its own mosquito control efforts – source reduction, larviciding and adult mosquito spraying,” said Kightlinger. “The West Nile epidemic of 2003 was unprecedented, and although we hope it never occurs again, we must prepare for another transmission season.”

     Forsch said the state will help communities prepare by offering a two-day educational seminar about creating and carrying out an effective mosquito control program on the local level. The seminar will build on the existing training offered through SDSU Cooperative Extension and will be scheduled in early 2004.