Abstract
Mosquitoes can transmit to humans devastating and deadly pathogens. As many chemical insecticides are banned due to environmental side effects or are of reduced efficacy due to resistance, biological control, including the use of bacterial strains with insecticidal activity, is of increasing interest and importance. The urgent actual need relies on the discovery of new compounds, preferably of a biological nature. Here, we explored the phenomenon of natural larvae mortality in larval breeding sites to identify potential novel compounds that may be used in biological control. From there, we isolated 14 bacterial strains of the phylum Firmicutes, most of the order Bacillales. Cultures were carried out under controlled conditions and were separated on supernatant and pellet fractions. The two fractions and a 1:1 mixture of the two fractions were tested on L3 and early L4 Aedes albopictus. Two concentrations were tested (2 and 6 mg/L). Larvae mortality was recorded at 24, 48 and 72 h and compared to that induced by the commercialized B. thuringiensis subsp. israelensis. Of the 14 strains isolated, 11 were active against the A. albopictus larvae: 10 of the supernatant fractions and one pellet fraction, and mortality increased with the concentration. For the insecticide activity prediction in three strains of the Bacillus cereus complex, PCR screening of the crystal (Cry) and cytolytic (Cyt) protein families characteristic to B. thuringiensis subsp. israelensis was performed. Most of the genes coding for these proteins’ synthesis were not detected. We identified bacterial strains that exhibit higher insecticidal activity compared with a commercial product. Further studies are needed for the characterization of active compounds.
Highlights
Diseases transmitted by arthropods participate in a major part to infectious diseases’ morbidity and mortality worldwide, and mosquitoes are number one in terms of public health importance, transmitting such deadly diseases as malaria (Anopheles), filariasis (Culex) and dengue (Aedes) that cause millions of deaths every year [1]
Since Bacillales are known for their entomopathogenic activity, we focused our study on strains belonging to the Firmicutes phylum, corresponding to 14 of the isolated strains that have been deposited in the CSUR collection of Institut Hospitalo-Universitaire (IHU)
The most active strain using the supernatant fractions was the 125 gite strain of the B. cereus complex with 94% larvae mortality. It was followed by L. fusiformis with 85% of mortality and by the strain 117 gite of the B. cereus complex with 80% and V. pantothenticus with 79% of larvae mortality
Summary
Diseases transmitted by arthropods participate in a major part to infectious diseases’ morbidity and mortality worldwide, and mosquitoes are number one in terms of public health importance, transmitting such deadly diseases as malaria (Anopheles), filariasis (Culex) and dengue (Aedes) that cause millions of deaths every year [1]. Several studies have been carried out by isolating large collections of Bacillus strains to explore their biological activities, including antibacterial, insecticide and others [1,3,13,14,15,16]. Most of these beneficial compounds are largely used in several medical or economic purposes, especially to control various diseases in animals, humans and plants, when applied as a biological control agent [13]. Different studies investigated the bacterial populations of breeding sites and their possible effects on mosquito larval populations [17]. We suspected that bacterial insecticide may explain this phenomenon and attempted to explore it
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