Effect of some bio-insecticides on fourth-instar larvae of Aedes aegypti

Abstract

This study aimed to evaluate the mortality rates caused by the fungus Beauveria bassiana and aqueous extracts of the leaves of Albizia lebbeck and Brassica oleracea var. botrytis at different concentrations against the fourth-instar larvae of Aedes aegypti mosquitoes, as well as to determine the LC50 value for each treatment to rank its effectiveness. The study concluded that the fungal concentration of 9 × 10⁶ spores/ml was the most effective in controlling fourth-instar larvae of A. aegypti mosquitoes, achieving a mortality rate of 66.3%. Conversely, the concentration of 1×10⁵ spores/ml was the least effective at 45.5%, with significant differences observed between the concentrations used in the experiment. The results obtained also showed that the highest mortality rate (65.3%) occurred 96 hours after treatment, and the lowest at 24 hours after treatment. Based on LC50 values, B. bassiana exhibited the highest efficacy (LC₅₀ = 2.15 spores/ml), followed by cauliflower extract (LC₅₀ = 23.8 ppm), while Albizia lebbeck extract showed the lowest efficacy (LC₅₀ = 157.6 ppm). The study also demonstrated that a 10,000 ppm concentration of aqueous extract of cauliflower leaves was the most effective in killing fourth-instar larvae of A. aegypti mosquitoes (62.1%), while a 1 ppm concentration was the least effective (13.3%), with significant differences observed between some of the concentrations used. The highest mortality rate for the cauliflower extract was observed 96 hours after treatment (39.3%) and the lowest mortality at 8 hours after treatment (6.6%). The results indicated a clear concentration- and time-dependent response for all treatments, with the fungus B. bassiana showing the highest potential as a biological control agent against A. aegypti larvae.

Keywords:

Aedes aegypti, Beauveria bassiana, Albizia lebbeck, Brassica oleracea, LC₅₀, biological control.