Efficacy of the vegetative cells of Lysinibacillus sphaericus for biological control of insecticide-resistant Aedes aegypti

Background: The control of Aedes aegypti is usually based on chemical insecticides, but the overuse of these compounds has led to increased resistance. The binary toxin produced by Lysinibacillus sphaericus in the final stages of sporulation is used for mosquito control due to its specificity against the culicid larvae; however, it has been proved that Ae. aegypti is refractory for this toxin. Currently, there is no evidence of the use of L. sphaericus vegetative cells for mosquito biocontrol. Therefore, in this study, the vegetative cells of three L. sphaericus strains were assessed against a field-collected Ae. aegypti, resistant to temephos, and the reference Rockefeller strain. Results: Vegetative cells of L. sphaericus 2362, III(3)7 and OT4b.25 produced between 90% and 100% of larvae mortality in the reference Rockefeller strain. Effective concentrations of each L. sphaericus strain for the four larval stages ranged from 1.4 to 2 x 107 CFU/ml. Likewise, a consortium of L. sphaericus assessed against a field-collected Ae. aegypti resistant to temephos and the Rockefeller strain caused 90% of larvae mortality. Concentrations of L. sphaericus consortium that resulted in larvae mortality of field-collected and Rockefeller Ae. aegypti ranged from 1.7 to 2.5 x 10(7) CFU/ml. The vegetative cells of L. sphaericus have no effect on the Ae. aegypti eggs and pupae. Conclusions: The vegetative cells of L. sphaericus are effective against Ae. aegypti larvae, meaning that it could be used in the biological control of these mosquito species. Since the L. sphaericus consortium was effective against temephos-resistant Ae. aegypti, vegetative cells could be an alternative to overcome insecticide-resistant populations. Further studies, should be conducted to reveal the mode of action and the toxic principle of L. sphaericus vegetative cells.