Abstract
BackgroundThe detrimental effects of chemical insecticides on the environment and human health have lead to the call for biological alternatives. Today, one of the most promising solutions is the use of spray formulations based on Bacillus thuringiensis subsp. israelensis (Bti) in insect control programs. As a result, the amounts of Bti spread in the environment are expected to increase worldwide, whilst the common belief that commercial Bti is easily cleared from the ecosystem has not yet been clearly established.Methodology/Main FindingsIn this study, we aimed to determine the nature and origin of the high toxicity toward mosquito larvae found in decaying leaf litter collected in several natural mosquito breeding sites in the Rhône-Alpes region. From the toxic fraction of the leaf litter, we isolated B. cereus-like bacteria that were further characterized as B. thuringiensis subsp. israelensis using PCR amplification of specific toxin genes. Immunological analysis of these Bti strains showed that they belong to the H14 group. We finally used amplified length polymorphism (AFLP) markers to show that the strains isolated from the leaf litter were closely related to those present in the commercial insecticide used for field application, and differed from natural worldwide genotypes.Conclusions/SignificanceOur results raise the issue of the persistence, potential proliferation and environmental accumulation of human-spread Bti in natural mosquito habitats. Such Bti environmental persistence may lengthen the exposure time of insects to this bio-insecticide, thereby increasing the risk of resistance acquisition in target insects, and of a negative impact on non-target insects.
Highlights
Since the fifties, the massive use of chemical insecticides in insect control programs, very effective in most cases, has led to serious environmental problems, including the long-term persistence of the toxicity in the environment, leading to the acquisition of resistance in exposed insects [1]
Bacillus thuringiensis subsp. israelensis (Bti) belongs to the Bacillus thuringiensis species that is usually isolated from the soil but can be found in many other habitats such like insects, stored grains, and the phylloplane of plants [30,31,32] it was described as a poor colonist of leaf surfaces [33]
The impact of such uncontrolled Bti residue on natural insect populations is a cause for concern, especially since leaf litter represents the main source of food for mosquito larvae
Summary
The massive use of chemical insecticides in insect control programs, very effective in most cases, has led to serious environmental problems, including the long-term persistence of the toxicity in the environment, leading to the acquisition of resistance in exposed insects [1]. The toxin is a combination of six main proteins aggregated into a solid crystal encased in the bacterial cell [4], exhibiting acute toxicity towards dipteran insects such as larval mosquitoes and black flies. Today, this bacterium is widely used for the preparation of commercial bio-insecticides [5] used in insect control programs. The amounts of Bti spread in the environment are expected to increase worldwide, whilst the common belief that commercial Bti is cleared from the ecosystem has not yet been clearly established
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
