Insecticidal Activity of Ageratum conyzoides (Asteraceae) Aqueous Extracts against the Grasshopper Zonocerus variegatus (Orthoptera: Pyrgomorphidae)

Ageratum conyzoides (Asteraceae) is an annual plant with insecticidal activity against some insect pests. The present study was designed to evaluate the insecticidal activity of aqueous extracts (infusion and maceration) of A. conyzoides against the pest grasshopper Zonocerus variegatus (Orthoptera, Pyrgomorphidae). Concentrations of 0, 10, 30, 100 & 300 µg/ml were prepared and administrated through injection to grasshoppers. Mortality rate was recorded for adult grasshoppers each day until the 9th day of treatment. Results revealed a significant increase (p < 0.05) of mortality rate with increasing concentrations of the two plant extracts. Plant extracts at 300 µg/ml induced 100.00 ± 0.00 percent mortality of adults Z. variegatus after 4 and 5 days for A. conyzoides infusion and maceration respectively. No mortality was registered after treatment with 0 & 10 µg/ml of the two plant extracts. Male mortality rate tended to be higher than that of female at the same concentration. Also, infusion tended to significantly increase (p < 0.05) mortality rate than maceration at the same concentration. Phytochemicals screening have shown that the presence of saponins, tannins, triterpenoids and alkaloids in the A. conyzoides aqueous extracts may be responsible for the insecticidal activity of this plant. These phytochemicals may therefore be exploited and serve as suitable alternatives to synthetic insecticides against the grasshopper Z. variegatus.