Larvicidal efficacy of monoterpenes against the larvae of Anopheles gambiae

ObjectiveTo evaluate the larvicidal efficacy of eight volatile components of essential oils against 3rd instar larvae of Anopheles gambiae s.s.MethodsLarvicidal effects of each compound were evaluated in both laboratory and semi-field trials. Stock solution was prepared and serial dilutions were made in six concentrations for each compound. A total of 20 larvae were exposed to larvicides for each replicate and monitored at intervals of 12, 24, 48 and 72 h. Larvae monitoring was done on basis of dead and live larvae in all intervals.ResultsAll assayed compounds were larvicides and presented varying degrees of larval toxicity, with LC50 values ranging from 1.28 to 1 938.92 mg/L depending on the treatment time (12, 24, 48 or 72 h). (−)-Perillyl alcohol presented the strongest larvicidal activity towards Anopheles gambiae larvae, with LC50 values of 73.60, 18.36, 1.72 and 1.28 mg/L after 12, 24, 48 and 72 h of exposure, respectively. The next strongest were (−)-isopulegol (LC50 = 135.10, 49.39, 34.39 and 20.22 mg/L) and (−)-carvone epoxide (LC50 = 168.86, 124.74, 80.84 and 23.46 mg/L). After 12, 24 and 48 h of treatment, hydroxydihydrocarvone was the least toxic compound, with LC50 values of 1 938.92, 1 172.18 and 401.03 mg/L, respectively.ConclusionsThe data obtained in this study suggest that all evaluated monoterpenes, especially (−)-perillyl alcohol, have remarkable larvicidal effects and may be considered as potential sources for the development of suitable natural larvicides for mosquito management programs. Further small-scale field trials should be conducted.