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 of Aedes 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 .

Graphical abstract

Background: Being a low-risk insecticide, plant essential oils emerge as competent mosquitocidal and repellent candidates. However, essential oil may act differently in different mosquito species and different developmental stages of same mosquito species. In the current investigation, we evaluated the ovicidal, larvicidal, adulticidal and repellent activities of essential oil extracted from the leaves of Lippia alba against two medically important mosquito species, Aedes aegypti and Culex quinquefasciatus. The efficacy of the oil was assessed under laboratory conditions against different developmental stages of the selected species. Results: From the findings, it can be inferred that L. alba oil is more effective as a repellent against both the targeted mosquito species. Results also demonstrated that ovicidal, larvicidal and repellent properties of the essential oil were higher against Culex quinquefasciatus than Aedes aegypti. GC-MS analysis of the oil showed the presence of aromadendrene oxide, caryophyllene oxide, etc. as major constituent compounds. Conclusion: The outcomes of this study clearly indicated that the essential oil of L. alba has the potentiality to act more effectively as a repellent, followed by a larvicidal agent against mosquito and at the same time the results revealed differential vulnerability of different mosquito species and their life stages against a particular plant essential oil.

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 .

Essential oil from the leaves of Aegle marmelos was investigated for their larvicidal, ovicidal, adulticidal and repellent properties against Aedes aegypti and Culex quinquefasciatus. Essential oil was extracted from the fresh leaves by hydro distillation method. Different concentrations of the oil were applied against different developmental stages of both the mosquito species. The result of different bioassay showed various responses between the species. The essential oil showed higher efficacy as larvicidal and adulticidal agent against Cx. quinquefasciatus (LC50=121.88ppm against larva and 121.50ppm against adult at 72 hour exposure) while as ovicidal and repellent agent, the essential oil showed higher efficacy against Ae. aegypti with LC50 value 278.82ppm at 72 hour and 1 hour of protection time respectively. Therefore, it can be inferred that this essential oil is a potential one which could further be used as mosquitocidal agent against both the mosquito species. The GC-MS analysis revealed the presence of β-terpinyl acetate, 5-isopropenyl-2-methyl-7-oxabicyclo (4.1.0) hepten-2-ol and 2,3-pinanediol as major probable constituents of the oil which might play major role against insecticidal activities of the plant oil.