Toxic and synergetic effect of plant essential oils along with nano-emulsion for control of three mosquito species

Nano-emulsion containing Eucalyptus grandis (W. Hill ex Maiden) and Corymbia citrodora (Hook.) K.D.Hill & L.A.S.Johnson (common synonym Eucalyptus citriodora Hook.) leaf essential oils individual, combination was evaluated its larvicidal activity against Anopheles stephensi, Aedesaegypti and Culex quinquefasciatus mosquito larvae at 24 h post treatment. Nano-emulsion had low polydispersivity index and mean droplet size was below 66 nm. After 24 h E. grandis essential oil exhibited significant larvicidal activity with LC₅₀ and LC₉₀ values in A. aegypti (23.667; 438.797 ppm in A. aegypti A. stephensi (10.984; 277.535 ppm) and C. quinquefasciatus (4.676; 106.415 ppm). Similarly in C. citrodora showed low LC₅₀ and LC₉₀ values in A. aegypti (18.430; 1048.599 ppm), A. stephensi (6.573; 176.737 ppm) and C. quinquefasciatus (7.917; 287.720 ppm) respectively. The combination of E. grandis and C. citrodora essential oils showed higher mortality rates than individual essential oils, with low LC₅₀ and LC₉₀ values in A. aegypti (3.625; 58.962 ppm), A. stephensi (3.245; 34.473 ppm) and C. quinquefasciatus (3.002; 30.153 ppm). Nano-emulsion exhibited toxic effects similar to combination group with LC₅₀ and LC₉₀ values in A. aegypti (5.344; 113.362 ppm), A. stephensi (3.183; 83.112 ppm) and C. quinquefasciatus (2.832; 166.665 ppm). Chemical constituents of both essential oil were analyzed using GC-MS and FT-IR, result showed E. grandis contain different compounds namely; alpha-pinene, (31.74%); o-cymene, (17.84%); Eucalyptol (16.24%); Bicyclo[2.2.1]heptane (3.2%) and C. citrodora showed Citronellol (49.31%); dl-Isopulegol (25.39%) as a major compound while their synergistic action may be due to type’s composition of EOs might produce the synergist effect along with nanoemulsions. Our findings suggest that combination of essential oil E. grandis and C. citrodora can be used for mosquito control as green approach.