Inhibition of Ascosphaera apis by citral and geraniol

In vitro tests showed that citral and geraniol inhibited the fungus Ascosphaera apis which causes chalkbrood disease in the honeybee, Apis mellifera. The vapors of 5 μl of citral or 10 μl of geraniol per culture dish prevented vegetative growth. Daily applications of 30 μl of citral per dish killed sporulated cultures within 48 hr. However, A. apis spores in dried larval remains (mummies) survived 96-hr exposure to the vapors of 30 μl of citral per dish per day.Vapors of a geranic and nerolic acid mixture, 2-heptanone, isopentyl acetate, octanoic acid, and citronella and melissa oils were less inhibitory than citral or geraniol. Potassium sorbate, sodium propionate, and tetracycline had no inhibitory effect when placed on the culture medium. Remains of larvae killed by American foulbrood disease caused only a slight reduction in the growth of A. apis.