A fellow reader, Wildbill, shared a tip in the comments that might help you decide which building to use your Bug Sprays on in the Luck of the Irish Griffins. I can’t test this as I’ve got all the drops I need but you might want to try it. 
From Wildbill:
“This works for me and hope it works for others, when trying to clear a building where a task is going on and bugs are on it, if you go to Mickey and click on the task, if the task is not complete the sprayer will show up over the building, if you click on the task and it is complete Peter will show up with the you must do this to do that bubble and it is ready to collect. With this you hopefully will not need to waste sprayers”.
Thanks again Wildbill.
~ Russian Tigger
Family Guy Addicts 