Insecticidal properties of extracts and phytochemicals isolated from three Egyptian plants against Culex pipiens

The chemistry of three Egyptian plants, namely Ambrosia maritima L., Achillea santolina L. and Adhatoda vasica L. was studied. Integration use of chromatographic methods led to isolate fifteen compounds of sesquiterpenes, flavonoids and alkaloids from these plants. The chemical structures of the isolated compounds were determined by using spectral data of ¹H NMR, ¹³C NMR, MS and UV.

In the preliminary test, the extracts and compounds were evaluated at concentration of 500mg/l against the fourth instar larvae of Culex pipiens. Among the tested extracts A. vasica alkaloidal fraction was the most effective with complete mortality of C. pipiens larvae followed by A. santolina extract which caused 43.3% mortality. Two sesquiterpenes (neoambrosin and damsin, and two flavonoids (santoflavone and eupatorin) and the alkaloid vasicine caused complete mortality of the larvae at this concentration. The extracts and compounds that display mortality higher than 50% were further evaluated at a series of concentration to calculate the lethal concentration values (LC₅₀). Eupatorin revealed the strongest toxicity with LC₅₀ with of 5.61mg/l. The alkaloid vasicine showed good insecticidal activity since LC₅₀ value was 88.88mg/l. Among the tested sesquiterpenes, damsin had the highest activity, followed by neoambrosin while hymenin was the less effective one. The obtained results suggest that eupatorin, neoambrosin, damsin and ambrosin may serve as new natural compounds for control C. pipiens.