Skin and oviposition deterrent, ovicidal and deleterious delayed mortality effects of α-amyrin acetate against the malarial vector Anopheles stephensi. (Diptera: Culicidae)
Keywords:Anopheles stephensi, Catharanthus roseus, oviposition deterrent, delayed mortality, gravid mortality, oviposition activity index
Selective discriminating behaviour of the ovipositing female for an appropriate oviposition habitat selection and the substances involved in oviposition site choice by vector mosquitoes have recently become a focal point of interest in the concept of integrated vector control management. In the current study, we isolated and identified α-amyrin acetate fromÂ Catharanthus roseusLinn (Apocynaceae) and assessed theÂ Â skin repellency, oviposition deterrency, ovicidal, gravid mortality and deleterious delayed mortality against the malarial vectorÂ Anopheles stephensiListon (Diptera:Culicidae). Water treated with the α-amyrin acetate had a high deterrent activity in ovipositing females: oviposition activity index values for the test species were -0.22, -0.38, -0.42 and -0.52 for α-amyrin acetate at concentrations of 0.007, 0.015, 0.025 and 0.050 p.p.m., respectively. High degrees of mortality were observed with various concentrations of α-amyrin acetate: 1.12 (control) to 7.20 for gravid females, and 0.62 (control) to 9.05 for oviposited females. The highest mortality in both gravid and oviposited females was observed soon after they came in contact with oviposition medium treated with the α-amyrin acetate, and this was found to be significant at doses higher than 0.015 p.p.m., suggesting possible contact toxicity of the α-amyrin acetate. The α-amyrin acetate had the most effective skin repellency with ED50Â and ED90Â values of 0.6659 and 1.7720Âµg/cm2Â with biting protection time of 3.5 h. The α-amyrin acetate caused moderate ovicidal activity against various age groups ofÂ A. stephensiÂ but it inflicted delayed effects such as high larval, pupal and adult mortality. The age of the eggs and the duration of the α-amyrin acetate treatment influenced the ovicidal activity observed. It is clear that α-amyrin acetate ofÂ C. roseusÂ can affect the oviposition cycle ofÂ A. stephensiListon, thereby suppressing the vector population and adversely influencing transmission of the disease pathogen.
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