Doungrat Riyong

Chemical Composition and Larvicidal Activity of Edible Plant-Derived Essential Oils Against the Pyrethroid-Susceptible and -Resistant Strains of Aedes aegypti (Diptera: Culicidae)

ABSTRACT: The chemical compositions and larvicidal potential against mosquito vectors of selected essential oils obtained from five edible plants were investigated in this study. Using a GC/MS, 24, 17, 20, 21, and 12 compounds were determined from essential oils of Citrus hystrix, Citrus reticulata, Zingiber zerumbet, Kaempferia galanga, and Syzygium aromaticum, respectively. The principal constituents found in peel oil of C. hystrix were &bgr;-pinene (22.54%) and d-limonene (22.03%), followed by terpinene-4-ol (17.37%). Compounds in C. reticulata peel oil consisted mostly of d-limonene (62.39%) and y-terpinene (14.06%). The oils obtained from Z. zerumbet rhizome had &agr;-humulene (31.93%) and zerumbone (31.67%) as major components. The most abundant compounds in K. galanga rhizome oil were 2-propeonic acid (35.54%), pentadecane (26.08%), and ethyl-p-methoxycinnamate (25.96%). The main component of S. aromaticum bud oil was eugenol (77.37%), with minor amounts of trans-caryophyllene (13.66%). Assessment of larvicidal efficacy demonstrated that all essential oils were toxic against both pyrethroid-susceptible and resistant Ae. aegypti laboratory strains at LC50, LC95, and LC99 levels. In conclusion, we have documented the promising larvicidal potential of essential oils from edible herbs, which could be considered as a potentially alternative source for developing novel larvicides to be used in controlling vectors of mosquitoborne disease.

Chemical Constituents and Combined Larvicidal Effects of Selected Essential Oils against Anopheles cracens (Diptera: Culicidae)

A preliminary study on larvicidal activity against laboratory-colonized Anopheles cracens mosquitos revealed that five of ten plant oils at concentration of 100 ppm showed 95–100% larval mortality. The essential oils of five plants, including Piper sarmentosum, Foeniculum vulgare, Curcuma longa, Myristica fragrans, and Zanthoxylum piperitum, were then selected for chemical analysis, dose-response larvicidal experiments, and combination-based bioassays. Chemical compositions analyzed by gas chromatography coupled to mass spectrometry demonstrated that the main component in the oil derived from P. sarmentosum, F. vulgare, C. longa, M. fragrans, and Z. piperitum was croweacin (71.01%), anethole (63.00%), ar-turmerone (30.19%), safrole (46.60%), and 1,8-cineole (21.27%), respectively. For larvicidal bioassay, all five essential oils exerted promising efficacy in a dose-dependent manner and different performances on A. cracens after 24 hours of exposure. The strongest larvicidal potential was established from P. sarmentosum, followed by F. vulgare, C. longa, M. fragrans, and Z. piperitum, with LC50 values of 16.03, 32.77, 33.61, 40.00, and 63.17 ppm, respectively. Binary mixtures between P. sarmentosum, the most effective oil, and the others at the highest ratio were proved to be highly efficacious with a cotoxicity coefficient value greater than 100, indicating synergistic activity. Results of mixed formulations of different essential oils generating synergistic effects may prove helpful in developing effective, economical, and ecofriendly larvicides, as favorable alternatives for mosquito management.

Synergy in the adulticidal efficacy of essential oils for the improvement of permethrin toxicity against Aedes aegypti L. (Diptera: Culicidae)

BackgroundIn a previous screening program for mosquitocides from local edible plants in Thailand, essential oils (EOs) of Cyperus rotundus, Alpinia galanga and Cinnamomum verum, were found to possess promising adulticidal activity against Aedes aegypti. With the aim of reducing usage of conventional insecticides and improving the management of resistant mosquito populations, this study was designed to determine the potential synergism in the adulticidal efficacy of EOs on permethrin toxicity against Ae. aegypti, both pyrethroid-resistant and -susceptible strains.MethodsEOs extracted from rhizomes of C. rotundus and A. galanga as well as C. verum barks were evaluated for chemical compositions and adulticidal activity against Muang Chiang Mai-susceptible (MCM-S) and Pang Mai Dang-resistant (PMD-R) strains of Ae. aegypti. Adulticidal bioassays of EO-permethrin mixtures for synergistic activity were also performed on these Ae. aegypti strains.ResultsChemical characterization by the GC-MS analytical technique demonstrated that 48 compounds were identified from the EOs of C. rotundus, A. galanga and C. verum, representing 80.22%, 86.75% and 97.24%, respectively, of all compositions. Cyperene (14.04%), β-bisabolene (18.27%) and cinnamaldehyde (64.66%) were the main constituents of C. rotundus, A. galanga and C. verum oils, respectively. In adulticidal bioassays, EOs of C. rotundus, A. galanga and C. verum were effective in killing Ae. aegypti, both MCM-S and PMD-R strains, with LD50 values of 10.05 and 9.57 μg/mg female, 7.97 and 7.94 μg/mg female, and 3.30 and 3.22 μg/mg female, respectively. The adulticidal efficacy against MCM-S and PMD-R Ae. aegypti of these EOs was close to that of piperonyl butoxide (PBO, LD50 values = 6.30 and 4.79 μg/mg female, respectively) but less pronounced than that of permethrin (LD50 values = 0.44 and 3.70 ng/mg female, respectively). Nevertheless, combination-based bioassays discovered the accomplished synergism of EOs together with permethrin. Significant synergistic effects with permethrin against both the strains of Ae. aegypti were recorded in the EOs of C. rotundus and A. galanga. Addition of C. rotundus and A. galanga oils decreased the LD50 values of permethrin against MCM-S dramatically from 0.44 to 0.07 and 0.11 ng/mg female, respectively, with synergism ratio (SR) values of 6.28 and 4.00, respectively. Furthermore, EOs of C. rotundus and A. galanga also reduced the LD50 values of permethrin against PMD-R drastically from 3.70 to 0.42 and 0.003 ng/mg female, respectively, with SR values of 8.81 and 1233.33, respectively.ConclusionsThe synergy of enhanced adulticidal toxicity recorded from EO-permethrin combinations against both strains of Ae. aegypti presents a promising role of EOs as a synergist for improving mosquitocidal efficacy, particularly in situations where conventional compounds are ineffective or inappropriate.