Laboratory evaluation of Dalbergia oliveri (Fabaceae: Fabales) extracts and isolated isoflavonoids on Aedes aegypti (Diptera: Culicidae) mosquitoes

We explored the potential of Burma rosewood, Dalbergia oliveri in dengue fever vector control by evaluating various extracts as larvicides and growth disruptors of Aedes aegypti Linnaeus (Diptera: Culicidae) under laboratory conditions. Third instars and pupae of the mosquito were tested using WHO guidelines. Highest larvicidal effect was obtained with dichloromethane and hexane extracts (LC50 = 289.1 and 325.3 ppm, respectively) within 24 h post-treatment. However, toxicity was about 1.78-fold more in dichloromethane extracts than hexane extract, if treatment was given for longer duration of 48 h (LC90 = 5048.5 ppm for hexane and 2848.1 ppm for dichloromethane extracts, respectively). In these treatments moderate inhibition of pupation was also seen with some larvae staying as 4th stage larvae for 8 days before dying. There were no significant differences in the sex ratio of emerged adults compared with the controls. Dichloromethane extract, being most active, was subjected to sequential chemical separation to obtain series of isoflavonoids. Three compounds (+)-medicarpin, formononetin and (±)-violanone were identified as active larvicides of Ae. aegypti. Significant pupal mortality was observed with dichloromethane extract treatment of 1–3 h old pupae after 48 h post-treatment (LC50 = 1004.5 ppm). Isoflavonoid medicarpin (LC50 = 296.72 ppm) was most active compound against pupae. Eclosion inhibition (EI) was also observed in pupae treated with dichloromethane extract (EI50 of 668.7 ppm). Thus, naturally occurring larvicides can be particularly effective where larval habitats are readily identifiable. Results obtained should be of value in the search for new natural larvicidal compounds from other extracts as well and represent the first report of this plant species being used to control a mosquito vector.

► This is the first report to show Dalbergia oliveri extracts and isoflavonoids therein are mosquitocidal, and effective against both larvae and pupae of Aedes aegypti.
► Effect on eclosion process after pupal treatment with DCM or EtOAc extracts was highly significant.
► The studies indicate that anti-eclosion activity was due to a common allelochemical present in both DCM and EtOAc extract and not the isoflavonoids, which is under investigation.