Developing Recombinant Bacteria for Control of Mosquito Larvae

Abstract

Genetic engineering techniques have been used to significantly improve mosquito larvicides based on the bacteria Bacillus thuringiensis (Bt) subsp. israelensis (Bti) and Bacillus sphaericus (Bs). These new larvicides hold excellent promise for providing better and more cost-effective control of nuisance mosquitoes and vectors of important diseases, including the anopheline vectors of malaria and culicine vectors responsible for filariasis and viral encephalitides. The toxicity of Bti and Bs is due primarily to endotoxin proteins produced during sporulation. After ingestion by larvae, these are activated and destroy the larval stomach, quickly resulting in death. By cloning the genes encoding various endotoxins from Bt and Bs species, and engineering these for high levels of synthesis, we have been able to generate recombinant bacterial strains based on Bti that are more than 10 times as effective as the conventional strains of Bti or Bs that serve as the active ingredients of commercial bacterial larvicides currently used for mosquito control. The best of these recombinants contain all major Bti endotoxins, specifically, Cry4A, Cry4B, Cry11A, and Cyt1A, plus the binary (Bin) endotoxin of Bs, the principal mosquitocidal protein responsible for the activity of this species. The presence of Cyt1A in these recombinants, which synergizes Cry toxicity and delays resistance to these proteins and Bs Bin, should enable long term use of these recombinants with little if any development of resistance. In the field, these new recombinants should be particularly effective larvicides against most important vectors and nuisance species of the genus Culex, the malaria vectors Anopheles gambiae and An. arabiensis, and species of Aedes and Ochlerotatus sensitive to Bs.

Cytopathological Effects of Bacillus sphaericus Cry48Aa/Cry49Aa Toxin on Binary Toxin-Susceptible and -Resistant Culex quinquefasciatus Larvae

“…Our data imply an interaction between the Cry48Aa and Cry49Aa components that results in a complex and specific combination of cytopathological effects resulting from the joint action of Bin and three-domain-protein-like insecticidal proteins. It has been demonstrated that resistance selection is inversely proportional to the number of toxins used, particularly those that interact with distinct receptors on midgut epithelial cells (11,12,28). The ability of Cry48Aa/Cry49Aa to overcome resistance makes this toxin a promising weapon in the armory of safe, insecticidal proteins with great potential for use as active ingredients of a new generation of biolarvicides for vector control that conjugate toxic factors with distinct sites of action.…”

Fate of Bacillus thuringiensis subsp. israelensis in the Field: Evidence for Spore Recycling and Differential Persistence of Toxins in Leaf Litter

“…As an increasing number of recombinant B. thuringiensis strains containing Cyt toxins are developed with the goal of obtaining a more efficient insecticidal product than B. thuringiensis subsp. israelensis (14,15), it is necessary to better characterize the fate of Cyt toxins in the environment.…”

Individual and combined effects of Bacillus thuringiensis var. israelensis, temephos and Leptolegnia chapmanii on the larval mortality of Aedes aegypti

“…It is therefore not surprising that the interest in alternative nonchemical strategies has increased in recent years. The use of biological control agents such as bacteria, protozoa, nematodes, and fungi has accordingly been developed with an attempt at gaining control over mosquito populations (Federici et al 2007). …”