Effect of synergist piperonyl butoxide (PBO) on the toxicity of some essential oils against mosquito larvae.

Effect of a known synergist piperonyl butoxide on the toxicity of steam distillate essential oils of Jamarosa (Cymbopogan nardus), Pacholli (Pogostemon pacholli), Basil (Ocimum basilicum), and Peppermint (Mentha pipreta) plant species against Anopheles stephensi larvae were evaluated. The purpose of the present study was to identify the insecticidal potential of these oils against mosquito larvae. The Piperonyl Butoxide (PBO) was used to enhance the activity of these oils with the aim of developing essential oil based formulations. The bioassays of these oils with and without PBO were performed against late 3rd instar larvae of An. stephensi. The LC50 values against An. stephensi were 44.19 ppm for Ocimum basilicum oil, followed by, Mentha pipreta, Cymbopogan nardus, and Pogostemon pacholli oil which gave LC50 values above 250 ppm. Thus in the present study the Ocimum basilicum oil was found to be most effective, whereas Pogostemon pacholli oil was found to least effective against mosquitoes for larvicidal action. The effect of synergist PBO led to the enhancement of toxicity of oils, the LC50 value for Ocimum basilicum were reduced from 44.19 ppm to 23.87 ppm. Similarly the oil of Pogostemon pacholli showed most significant results where the LC50 value was >250 ppm it was reduced to 50 ppm with PBO.