Abstract
BackgroundThe 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.ResultsVegetative 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 × 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 × 107 CFU/ml. The vegetative cells of L. sphaericus have no effect on the Ae. aegypti eggs and pupae.ConclusionsThe 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.
Highlights
The control of Aedes aegypti is usually based on chemical insecticides, but the overuse of these compounds has led to increased resistance
Activity of L. sphaericus on Ae. aegypti Rockefeller strain The three L. sphaericus strains showed a similar percentage of hatched eggs compared to the positive control, and these groups were statistically different from the negative control, showing that treatment had no effects on egg hatching (Kruskal-Wallis: χ2 = 10.71, df = 4, P = 0.02) (Fig. 1a)
Since Ae. aeypti larvae are refractory to Bin toxins and vegetative cells exhibit a diverse collection of toxic proteins, we suggest that L. sphaericus vegetative cells could be used to control Ae. aegypti populations
Summary
The control of Aedes aegypti is usually based on chemical insecticides, but the overuse of these compounds has led to increased resistance. The overuse of compounds such as DDT, malathion, and temephos has led to the development of insecticide resistance [1, 2]. Another issue to be considered is the negative ecological effect of these insecticides [3]. Since the re-invasion of Ae. aegypti in the 1960s, prevention against the diseases transmitted by this mosquito is based on the use of chemical insecticides [5].
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