Effect of Rhazya stricta, Calotropis procera, and Francoeuria crispa on Larvae and Eggs of Culex pipiens

Abstract

ABSTRACT Toxicity of the aqueous extracts of Rhazya stricta Decne, Calotropis procera (Ait.) Cass., and Francoeuria crispa (Forssk.) R.Br. leaves against larvae of Culex pipiens L. mosquitoes was investigated by incorporating the extracts into egg and larval rearing media. Acute LC50 were 270 and 322 ppm for R. stricta and C. procera, respectively. The chronic toxicities for R. stricta at concentrations 0.02 and 0.04 percent, reached 70 and 100 percent larval mortality, respectively, and 91.1 and 100 percent at concentrations of 0.05 and 0.075 percent, respectively, for C. procera. Both materials conferred significantly reduced larval development and thus, consequently reducing pupation and adult emergence. Only 10 and 33.3 percent of the larvae reared in media containing 0.02 percent of R. stricta water extract and 0.025 percent of C. procera completed development to the pupa stage. None of the larvae in R. stricta extract reached adulthood and only 20 percent of the larvae did in the C. procera extract. The highest concentration of F. crispa tested (0.25%) caused only 55.3 percent mortality after 10 days, leading to 34.3 and 21.2 percent successful pupation and adult emergence, respectively. No mosquito eggs were laid in media containing at concentrations ≥ 0.05 percent aqueous extract from any of the three plants. Application of R. stricta and C. procera extracts applied to mosquito larval breeding sites may well provide an environmentally safe method for control of mosquito populations.