The genus Cinnamomum

Pharmacology and Toxicology of Cinnamon and Cassia 275
minimal lethal concentration (MLC), and exposure duration for fungicidal action
at MIC and higher doses. Aspergillus fumigatus was the most susceptible and the
H. capsulatum and Candida species were most resistant. The MIC varied from
16–40 ppm. They have suggested that vapour inhalation of cinnamon oil could be
useful in the treatment of respiratory tract mycosis. Inoneye et al. (2000) studied the
inhibitory effect of essential oil on apical growth of A. fumigatus by vapour contact.
The results showed that the growth of the fungus was retarded at 63 g oil/ml of
air concentration.
Insecticidal activity
The use of plants or extracts of plants to control, repell or to eradicate pests and
harmful insects stretches back over the agricultural history of mankind. Many of the
plant-derived insecticides, insect repellants and antifeedants have the advantage that
while being toxic to the pests, they are nontoxic to humans. Studies conducted in
different laboratories have shown promising results with cinnamon and cinnamon oil
in pest control (see Table 11.3). Gracia (1990) studied the effect of the extracts of
cinnamon and cinnamon oil toxicity, repellency, growth inhibition and ovicidal
actions on the bean weevil Callosobruchus chinensis. The petroleum-ether extract and oil
were found to be toxic to the bean weevil with an LD 50 of less than 200 mg/ml.
Cinnamon oil showed fumigation action, which caused 100% mortality at 50 mg of
100% oil in 40 cc of space. Both petroleum and alcoholic extracts exhibited concentration-dependent
repellent action. Cinnamon oil could be used for the management
of honeybee diseases. The results of the study by Calderon et al. (1994) on Bacillus
laevis, the causative agent of American foulbrood diseases, have shown that the oil
completely inhibited the growth at 10 ppm level for 72 hours, Ascosphaera apis at
100 ppm for 168 hours and Bacillus alvei at 10 ppm for 72 hours. Floris et al. (1996)
also investigated the same problem and extended the study to field trials and obtained
beneficial results. The oil was tested in nutrient broth and found that the minimal
bactericide concentration was 50 mg/kg and the sporicide concentration was
100 mg/kg. The oil at 400 mg/kg concentration was found to be nontoxic to adult
bees. In field trials, they administered the oil in solid food and it was effective at a
concentration of 400 mg/kg. Another beneficial activity of cinnamon oil obtained
from the studies by Hauhong and Shan Huan (1994) was the complete inhibition of
the reproduction of Sitophilus zeamais, Rhyzopertha dominica (lesser grain borer) and
Tribolium castaneum (flour beetle) at a concentration of 0.1–0.2% mixed with wheat
or wheat flour. Topical application of oil at a concentration of 0.1–0.5 l/larva
effectively inhibited the growth of larvae of Tenebrio molite. The active constituent
producing the inhibitory action was found to be cinnamaldehyde. The same authors
studied the effect of the oil from another species of cinnamon (C. micranthum) and
found that it inhibited the growth of T. castaneum effectively in stored crops and that
the oil was safe for mammals even at high concentrations (Hauhong and Shan Huan,
1996). The antifeedant effect of cinnamaldehyde against the grain storage insects
Tribolium castaneum and Sitophilus zeamais was studied by Huang and Ho (1998). A
methylene chloride extract was insecticidal to both the insects. (The contact fumigant
and antifeedant effects were also tested and found to have an LC 50 value of 0.7 mg
cm 2 and LC 95 of 0.9 mg cm 2 .) However, T. castaneum had a higher fumigant toxicity
than S. zeamais (LC 50 0.28 mg cm 2 and 0.54 mg cm 1 respectively). The adults