For the first time since 2012, the city of Manchester sprayed for mosquitoes in more than 20 city-owned locations.Four crews worked Tuesday to reduce the mosquito population in Manchester after nine batches of mosquitoes tested positive for West Nile virus.>> Download the free WMUR appThe spraying started around 6 p.m. and was expected to continue until midnight to help control the spread of the virus. “We are looking to kill adult mosquitoes -- the ones that are positive -- and hopefully we can break that cycle in time for the end of the season,” said Phil Alexakos, of the Manchester Health Department. “We are targeting schools, parks and athletic fields where the kids are going to be congregating and where sports are played, practices, so forth,” said Sarah McGregor, of Dragon Mosquito Control. The spraying was done using backpacks, in addition to a mounted sprayer on a truck for larger sites. “The air is thick with humidity, and that is perfect mosquito weather. They can survive a lot longer when there is moisture in the air,” McGregor said. Signs were placed at each location to inform residents, and crews made sure each place was vacated. “We like people to vacate the grounds while we are spraying so that no one is exposed,” McGregor said. Experts say a city-wide spray is not needed at this point but that residents should make sure they are not breeding mosquitoes on their property. “Buckets, containers, tarps, the kiddie pool, dog bowls, bird baths -- they are all breeding mosquitoes this time of year, and every mosquito has the potential of carrying West Nile right now,” McGregor said. McGregor also recommended wearing mosquito repellant and long pants and sleeves when outside.