Stagecoach say they are monitoring the 12 service following the latest incident in Lincluden, but there are urgent calls to halt the attacks.
Lincluden Community Council chairman Malcolm Campbell said: “Stagecoach have got to put their drivers’ and passengers’ safety at the foremost.
“They’ve got to make sure they’re safe, and if they don’t think they’re going to be safe I can just see this service being cancelled, to be honest.
“And it’s going to be a shame because there’s a lot of elderly people during the day who use this service.”
An object was again hurled at a bus on Lincluden Road at about 7.15 pm on Sunday, smashing a window.
It comes after previous incidents on Priory Road at about 12.55 pm on Tuesday April 11 and 6.40 pm on Saturday April 8.
On all three occasions, a small group of youths approximately 12 years of age are thought to be responsible.
Mr Campbell said: “I have spoken to some kids and they keep repeating that there’s nothing to do, but that’s not acceptable.
Pointing to the potential dangers, such as a driver swerving into oncoming traffic, he added: “It’s just unthinkable what might happen, with a windscreen getting smashed or something.”
Mr Campbell notes the 12 service is very popular, running from Lincluden into the centre of town and back and proving a link to the hospital.
Stagecoach are assisting police with enquiries, and a spokeswoman for the firm said: “Safety is our priority.
“However, we will continue to run the service as normal but will monitor the situation closely.”
She added: “These vandals are putting the safety of our passengers and drivers at risk.”
PC Richard Davidson warned the outcome could have been very different and said: “I am asking anyone who knows the identity of these youths contact Police Scotland on 101 before someone gets hurt.”