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Persistence and Recycling of Bioinsecticidal Bacillus thuringiensis subsp. israelensis Spores in Contrasting Environments: Evidence from Field Monitoring and Laboratory Experiments
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Edité par CCSD ; Springer Verlag -
International audience. Sprays of commercial preparations of the bacterium Bacillus thuringiensis subsp. israelensis (Bti) are widely used for the control of mosquito larvae. Despite an abundant literature on Bti field efficiency on mosquito control, few studies have evaluated the fate of spores in the environment after treatments. In the present article, two complementary experiments were conducted to study the effect of different parameters on Bti persistence and recycling, in field conditions and in the laboratory. First, we monitored Bti persistence in the field in two contrasting regions in France: the Rhône-Alpes region, where mosquito breeding sites are temporary ponds under forest cover with large amounts of decaying leaf matter on the ground, and the Mediterranean region characterized by open breeding sites such as brackish marshes. Viable Bti spores can persist for months after a treatment, and their quantity is explained both by the vegetation type and by the number of local treatments. We found no evidence of Bti recycling in the field. Then, we tested the effect of water level, substrate type, salinity, and presence of mosquito larvae on the persistence/recycling of Bti spores in controlled laboratory conditions (microcosms). We found no effect of change in water level or salinity on Bti persistence over time (75 days). Bti spores tended to persist longer in substrates containing organic matter compared to sand-only substrates. Bti recycling only occurred in presence of mosquito larvae, but was unrelated to the presence of organic matter.
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