Abstract:
Mosquitoes are vectors of many severe diseases, including malaria, yellow as well as
dengue fever, and lymphatic filariasis. The use of synthetic chemical insecticides for mosquito control
has been associated with resistance development and detrimental human, and ecological effects.
For a safer alternative, the emulsified Ocimum kilimandscharicum oil formulation was evaluated for
its larvicidal activity. The oil was analyzed by GC and GC/MS. The formulations were evaluated
against third instar mosquito larvae in the laboratory and later compared with Bacillus thuringiensis
subsp. israelensis against An. gambiae under field-simulated conditions. Thirty-nine compounds were
identified in the oil, the main ones being D-camphor (36.6%) and limonene (18.6%). The formulation
showed significant larval mortalities against An. gambiae and An. arabiensis larvae with LC50 of 0.07
and 0.31 ppm, respectively, at 24 h. Under the field-simulated trial, within 24 h, the formulation
showed 98% mortality while Bti had achieved 54%. On day three, it caused 100% mortality while
Bti achieved 76.5%. The high bioactivity and sublethal toxic effects to offspring of treated mosquito
larvae, in terms of disruption of larval morphological aspects, suggest the high potential of the
formulation as a botanical larvicide. The formulation, thus, may provide a valuable alternative for
the effective and eco-friendly control of disease vectors.
