A strain of Clostridium bifermentans individualized as serovar malaysia (C.b.m.) according to its specific H antigen is toxic to mosquito and blackfly larvae when given orally. The toxicity occurs in sporulated cells which contain, in addition to spores, proteinic parasporal inclusion bodies and feather-like appendages; the amino acid content of the inclusion bodies is similar to that of Bacillus thuringiensis serovar israelensis (B.t.i.) and B. sphaericus crystals. The toxicity to Anopheles stephensi is as high as that of B.t.i. and the best strains of B. sphaericus. Culex pipiens is somewhat less susceptible, and Aedes aegypti much less. Pure parasporal inclusion bodies, isolated by ultracentrifugation on sucrose gradients, are highly toxic to mosquito larvae. The larvicidal power is destroyed by heating at 80 degrees C or by treatment with 50 mM NaOH. It is preserved by freeze-drying. The innocuity to mice of the sporulated cells is shown by different routes of administration: force-feeding, percutaneous, subcutaneous, intraperitoneal or intravenous injections. The potential for the biological control of mosquito and blackfly larvae is suggested.
A novel Clostridium bifermentans strain toxic to mosquito larvae on ingestion was isolated from a soil sample collected from secondary forest floor. This strain was designated as serovar paraiba (C. b. paraiba) according to its specific H antigen. Clostridium bifermentans paraiba is most toxic to Anopheles maculatus Theobald larvae (LC50 = 0.038 mg/liter), whereas toxicity to Aedes aegypti (Linn.) (LC50 = 0.74 mg/liter) and Culex quinquefasciatus Say (LC50 = 0.11 mg/liter) larvae was 20 and 3 times lower, respectively. The toxicity to An. maculatus larvae is as high as that of Bacillus thuringiensis serovar israelensis. C. b. paraiba was also found to exhibit significant per os insecticidal activity toward adult Musca domestica (Linn.).