Natural Remedies in the Fight Against Insects

Abstract

With the discovery and large-scale use of synthetic insecticides in the 1940s and 1950s, the control of insects was mainly based on chemicals until the publication of the book “Silent Spring” by Rachel Carson. This new “green” move- ment was the driving force to search for new environmental compatible tools in the fight against pest and vector insects. There aremany bacteria knownwhich are causing insect diseases and used in insect control programs. Typical for these bacteria is the production of protein crystals the so-called d-endotoxins which are produced by the bacilli during sporulation. Two groups of bacteria are of importance: a) Bacillus thuringiensis (B.t.) and B. sphaericus. B.t. products are most widely used in insect control programs. Thousands of B.t. isolates are known which are grouped into three major pathotypes: – Pathotype A: lepidopteran specific Bacillus thuringiensis strains such as B.t. H-3a/3b (B. t. kurstaki); – Pathotype B: nematoceran specific strains such as B.t. H-14. (B. t. israelensis), which kill especially mosquito and blackfly larvae and some members of the suborder nematocera; -Pathotype C: coleopteran specific strain B.t. H-8a/8b (B. t. tenebrionis). The use of insect-specific toxins from Bacillus thuringiensis and B. sphaericus is forming an increasingly component of biological control strategies against nuisance, pest or vector species. The discovery of these microbial control agents marked the breakthrough in biological control, because of the special abilities of these microbial agents. Their protein crystals are highly toxic to target organisms and extremely environmentally safe. In Germany for instance, over 1,000 km2 of breeding sites have been treated with Bacillus thuringiensis israelensis and B. sphaericus resulting in a reduction of mosquito population year by year more by than 90% and without evidence of any harmful impact on the environment.