Effects of Eucalyptus citriodora essential oil and its major component, citronellal, on Haemonchus contortus isolates susceptible and resistant to synthetic anthelmintics

This study aimed to evaluate the effects of Eucalyptus citriodora essential oil and citronellal on a Haemonchus conforms isolate susceptible to anthelmintics, the Inbred-susceptible Edinburgh (ISE) and a resistant Kokstad isolate. The oil was analyzed by gas chromatography (GC). The products were evaluated using an egg hatching test (EHT), a larval development test (LDT) and an adult worm motility test (AWMT). The effective concentrations to inhibit 50% (EC50) of egg hatching and larval development and resistance ratios (RRs) were calculated. The results were analyzed by analysis of variance and Tukey's or Bonferroni's test. The major constituent of E. citriodora oil was citronellal (63.9%). According to EHT, EC50 values for the ISE isolate were 0.4 mg/ml and 0.3 mg/ml; for the Kokstad isolate, values were 0.5 mg/ml and 0.4 mg/ml for oil and citronellal, respectively. LDT EC50 values were 2.9 mg/ml and 2.3 mg/ml for the ISE isolate and 3.2 mg/ml and 2.4 mg/ml for the Kokstad isolate for oil and citronellal, respectively. In AWMT, 2 mg/ml of oil and citronellal completely inhibited the motility of both the ISE and Kokstad isolates. RRs between the isolates ranged from 1 to 1.3. No significant differences were observed between the isolates or treatment comparisons (P > 0.05). Therefore, E. citriodora oil and citronellal both exhibited ovicidal and larvicidal effects and inhibited the motility of both H. conforms isolates.