The bacterium Bacillus sphaericus is best-known to entomologists because of the toxicity of some strains to the larval stages of mosquitoes Taxonomy Identification of a bacterium as a B. sphaericus isolate is based on relatively few morphological features (e.g., the possession of a spherical terminal spore) and a limited number of biochemical tests (e.g., inability to ferment sugars). As a result, the classification contains a heterogeneous collection of strains and it has been shown that, at the DNA level, these can be divided into 5 major homology groups (groups I-V), each of which could be considered as a separate species. All of the insecticidal strains of B. sphaericus are found within a subdivision of one of these groups, Group IIA. However, not all strains that fall within this group are insecticidal. It is the insecticidal strains of B. sphaericus and their properties that will be considered further below