Toxicity of Individual and Blends of Pure Phytoecdysteroids Isolated from Vitex Schiliebenii and Vitex Payos against Anopheles Gambiae S.S. Larvae
Four phytoecdysteroids: (20-hydroxyecdysone-20, 22-monacetonide (1), 20-hydroxyecdysone (2), stigmasterol (3), gamma-sitosterol (4), were investigated for toxic effect against 3rd /4th instar larvae of Anopheles gambiae under laboratory conditions as individual compounds and in blends. The test larvae were treated with solutions containing the phytoecdysteroids of concentrations 1, 5 and 10ppm. The blends were prepared in the ratio of 1:1. Compounds 1 and 2, isolated from acetone extracts of Vitex payos caused 100% mortality at 10ppm. Compound 3 isolated from acetone leaves of V. schiliebenii and compound 4 isolated from acetone stem bark of V. schilebenii also showed potent activity against the larvae at 10ppm. At the lower concentrations, abnormal mobility and impaired development was observed. Phytoecdysteroids (20-hydroxyecdysone-20, 22-monacetonide (1) and 20-hydroxyecdysone (2) are larvicidal against An. gambiae. stigmasterol (3), gamma-sitosterol (4) also show potent IGR activities against An. gambiae. Also addition of compounds 1 and 2 to stigmasterol (3) and gamma-sitosterol (4) seperately improved the activity of the two compounds.