Toxicity of the aqueous leaf and Stem-bark extracts of <em>Annona muricata </em>to the 4<sup>th</sup> instar larvae of <em>Aedes aegypti</em>

Abstract

The crude aqueous extracts were tested against the fourth instar larvae of Aedes aegypti (Diptera: Culicidae) at five concentrations of the technical material ranging from 12.5-200 µg/ml, including control. The bioassays were carried out in the laboratory at temperature of 29◦C ± 2 and 29.5 ± 5% relative humidity. Four replicates of each concentration of the respective toxicants in a Completely Randomised Design (CRD) were introduced with ten fourth instar larvae of Ae. Aegypti. Mortality resulting from eclosion inhibition was monitored at 3-hours interval for a period of 3, 6, 9, 12- and 24-hours post treatment. Data collected were analyzed using log-probit regression and analysis of variance. Results showed that mortality increased with increase in time and concentration and these were significantly different (P<0.05). Results indicated 65% and 87.1% mortality at the highest concentration (200 µg/ml) of the leaf and stem-bark aqueous extract respectively while the least concentration (12.5 µg/ml) resulted in 19.4% and 38.7% respectively. The LC50 values were 92.5 µg/ml and 26.5 µg/ml for the leaf and stem-bark aqueous extract respectively while the LT50 values were 29.7hr and 53.9hr respectively for the leaf and the stem-bark aqueous extract. The study suggests that Annona muricata leaf and stem-bark aqueous extract has shown promise as biopesticide for Ae. Aegypti larvae control. However, the stem-bark was found to be more effective compared to the leaf aqueous extract.