REPELLENCY EFFECT OF SOME PLANT EXTRACTS AGAINST THE DENGUE VECTOR Aedes aegypti LINNAEUS 1762 (DIPTERA: CULICIDAE) WITH REFERENCE TO MODE OF ACTION AND RELATED FACTORS

The repellent activity of Annona squamosa, Ocimum basilicum and Piper nigrum with Azadirachta indica as a standard was determined against adult Aedes aegypti mosquitoes. Bioassay was conducted on laboratory reared Swiss albino mice by topical application at a fixed concentration of 0.01%. Crude aqueous aerial extracts of Annona squamosa, Ocimum basilicum, Piper nigrum and Azadirachta indica repelled the test mosquitoes. No mosquito repellence was observed in the control, and all mosquitoes took feed. The number of mosquitoes repelled, landed and fed on the control and crude aerial extracts was statistically and significantly different (P=.05). The protection time offered by the tested aerial extracts against Aedes aegypti were 150, 210, 240 and 300 minutes for Annona squamosa, Ocimum basilicum, Piper nigrum and Azadirachta indica respectively. The maximum percent protection offered by the aerial extracts was 64, 76, 88 and 92 respectively, and its respective repellent quotient values obtained on treatment against Aedes aegypti were 0.6, 0.7, 0.8 and 0.9. The efficacy of the phytoextracts when tried on topical application depended upon significant factors like absorption, adsorption and evaporation, which might have certainly played a crucial role in the persistence of the phytoextract repellent. Further, extraction of bioactive compounds, and evaluation of the same with the above mentioned key factors would aid in the development and advancement of suitable phytorepellents.