Larvicidal Activity of Pistia stratiotes (Water Lettuce) against Larvae of Aedes aegypti

The present investigation assesses the larvicidal effect of Pistia stratiotes (water lettuce) against early 3rd and 4th instar larvae of Aedes aegypti in the laboratory. Mosquito larvae were sampled and larval population was monitored before and after application of plant aqueous extract. To assess the larvicidal activity, four different doses (0.5, 1.0, 1.5 and 2.0) mg/L respectively were used in the trials. Larval mortality was monitored after 24, 48 and 72 hours. At the highest dose, mortalities of 97.40, 98.80 and 99.80% for the third instar larvae and 99.70, 97.50 and 97.7% for the fourth instar larvae was observed. The percentage mortality for the fourth instar larvae decreased with hours of exposure. Analysis of variance (ANOVA) conducted on the data, showed that there was significant difference (p>0.05) in mortality between treatments and in hours of exposure. Further, the LC50 and LC90 for the 3rd were 0.11 and 1.44 mg/L while that of the 4th instar larvae were 0.22 and 1.51 mg/L respectively. The study indicated that (P. stratiotes is an effective insecticide against the larvae of A. aegypti. Measures to enhance its use for large scale mosquito control are essential.