American foulbrood infection level in challenged colonies with and without a propolis envelope. Overall severity scores (0 = 0 cells in comb containing sign of AFB; 1 = 1–5 cells; 2 = 6–25 cells; and 3 =≥ 26 cells per comb) were compared between challenged colonies with and without a propolis envelope using Mann-Whitney U test (α = 0.05). Three out of five challenged colonies with a propolis envelope and four out of five challenged colonies without a propolis envelope showed signs of AFB infection in both August and September. High interquartile range in September in challenged colonies with a propolis envelope was a result of one colony showing a high AFB infection score level compared to all others. All colonies, in both challenged treatment groups, showed signs of AFB infection in October.