What kind of rapport do you have with the neighbor? Good? If so ask him to spray real early in morning or real late in evening. Better yet screen your bees in while he is spraying if you are concerned. I would not get upset about it anyway, especially if he is not upset about the bees in his birdbath or on his lawn. Hopefully they are not working the blooms and it also depends on the spray. I know I have read here you can spray round-up around hives with no worry.