Mosquitocidal potential of silver nanoparticles synthesized using local isolates of Bacillus thuringiensis subsp israelensis and their synergistic effect with a commercial strain of B-thuringiensis subsp israelensis

Control of larval stages of Aedes aegypti is considered an effective approach for preventing outbreaks of dengue fever. In this work, silver nanoparticles (Ag NPs) were synthesized using the supernatant and insecticidal proteins from local isolates of Bacillus thuringiensis subsp. israelensis (Bti). Mosquitocidal activity assays against A. aegypti larvae revealed that the highest toxicity was obtained from the Ag NPs synthesized using supernatant of Bti K55 and the inclusion proteins of Bti K46 with a lethal concentration 50 (LC50) of 0.001 and 0.008 mu g/mL, respectively. The synthesized nanoparticles were characterized using UV-vis absorption spectrophotometry, scanning electron microscopy (SEM), SEM coupled with energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier-transform infrared spectroscopy. The synergistic studies revealed that the Ag NPs synthesized using supernatant of Bti K55 were synergized with commercial Bti cells with a synergistic factor (SF) of 3.3 and 10.0 for LC50 and LC90, respectively. In addition, the Ag NPs synthesized using inclusion proteins of Bti K46 were synergized with commercial Bti cells with a SF of 1.6 and 4.2 for LC50 and LC90, respectively. This study provided the first report of the synergistic effect between Bti and Ag NPs. Such a combination could represent an effective approach for the control of the dengue vector and possibly reducing the likelihood of increased insect resistance to chemical control.