Mosquitocidal activity of twenty-eight plant essential oils and their binary mixtures against Culex quinquefasciatus, (Diptera: Culicidae).

BACKGROUND: Mosquito control programme using synthetic insecticides has been facing the challenges of resistance development. However, synergistic combinations of plant essential oils (EOs) having different modes of actions and potent lethal toxicity may further negate the concern of resistance development. METHODS: In this study, the toxicity of 28 EOs and the two synthetic insecticides, Temephos and Malathion were evaluated individually and based on the performance, binary combinations of effective EOs were prepared and tested against the larval and adult stages of Culex quinquefasciatus. Mixtures were prepared by blending LC10 or LD10 concentration/doses of candidates at different volume ratios. RESULTS: Results demonstrated that among 155 numbers of combinations of different volume ratios, 1:1 ratio of A. sativum (bulbs) L.+C. paradisi (peels) Macfd. (AsB + CpP) was found to be the most potent against adults, whereas, 1:1 volume ratio of Allium sativum (bulbs)+ Citrus paradisi (leaves) (AsB + CpL) was found to possess highest activity against larvae after considering its dose and synergistic interaction. GC-MS analysis revealed the presence of diallyl trisulfide, diallyl disulfide, beta-citronellol, ocimene as major constituents of AsB + CpP combination and diallyl disulfide, linalool, citronellal, caryophyllene oxide etc. in AsB + CpL combination. CONCLUSIONS: Therefore, the said mixtures of the plant essential oils and or mixtures of the constituent compounds can be used as effective control agents for the control of the filarial vector, C. quinquefasciatus.

Insecticidal activities of Citrus aurantifolia essential oil against Aedes aegypti (Diptera: Culicidae).

BACKGROUND: In the recent time, global attention for the control of vectors has shifted from chemical insecticides to botanicals. In the present investigation, authors attempted to evaluate the efficacy of peel and leaf essential oil (EO) of Citrus aurantifolia against Aedes aegypti. RESULTS: The results revealed that both the oils possess more ovicidal activity (LC50 value of 5.26 ppm and 17.71 ppm for leaf and peel oil respectively at 72 h) than larvicidal activity. As larvicide, the essential oil from the peel of Citrus aurantifolia showed rapid effect with LC50 value of 128.81 ppm at 24 h which reduced to 106.77 ppm at 72 h while the leaf oil showed slow effect with LC50 value of 188.59 ppm, 107.37 ppm and 104.59 ppm at 24 h, 48 h and 72 h respectively. Again, the two essential oils did not show significant adulticidal activity. GC-MS analysis of both the oils recorded presence of different compounds. As a major constituent compound of the leaf EO of Citrus aurantifolia, citral was tested for their ovicidal, larvicidal and adulticidal activities against Aedes aegypti. The result showed highest ovicidal activities (LC50 value of 4.84 ppm at 72 h) of citral followed by larvicidal (LC50 value of 87.02 ppm at 24 h) and adulticidal (LC50 value of 103.88 ppm at 24 h) activities. CONCLUSION: From this study, it can be concluded that the essential oil extracted from the leaf and peel of Citrus aurantifolia and one of its major constituent compound citral can be included in the mosquito control programme of Aedes aegypti.

Combinations of Plant Essential Oil Based Terpene Compounds as Larvicidal and Adulticidal Agent against Aedes aegypti (Diptera: Culicidae).

Insecticidal plant-based compound(s)in combinations may show synergistic or antagonistic interactions against insect pest. Considering the rapid spread of the Aedes borne diseases and increasing resistance among Aedes population against conventional insecticides, twenty-eight combinations of plant essential oil-based terpene compounds were prepared and tested against larval and adult stages ofAedes aegypti. Initially five plant essential oils (EOs) were assessed for their larvicidal and adulticidal efficacy and two of their major compounds from each EO were identified from GC-MS results. Identified major compounds namely Diallyldisulfide, Diallyltrisulfide, Carvone, Limonene, Eugenol, Methyl Eugenol, Eucalyptol, Eudesmol and α-pinene were purchased and tested individually against A. aegypti. Binary combinations of these compounds were then prepared using sub-lethal doses, tested and their synergistic and antagonistic effects were determined. The best larvicidal compositions were obtained while Limonene was mixed with Diallyldisulfide and the best adulticidal composition was obtained while Carvone was mixed with Limonene. Commercially used synthetic larvicide "Temephos" and adulticide "Malathion" were tested individually and in binary combinations with the terpene compounds. The results revealed that the combination of Temephos and Diallyldisulfide and combination of Malathion and Eudesmol were the most effective combination. These effective combinations bear potential prospect to be used against Aedes aegypti.