Clostridium bifermentans serovar malaysia (C.b.m.) is highly toxic to mosquito larvae. In this study, the following aquatic nontarget invertebrates were treated with high C.b.m. concentrations (up to 1,600-fold the toxic concentration for Anopheles stephensi) to study their susceptibility towards the bacterial toxin: Planorbis planorbis (Pulmonata); Asellus aquaticus (Isopoda); Daphnia pulex (Cladocera); Cloeon dipterum (Ephemeroptera); Plea leachi (Heteroptera); and Eristalis sp., Chaoborus crystallinus, Chironomus thummi, and Psychoda alternata (Diptera). In addition, bioassays were performed with mosquito larvae (Aedes aegypti, Anopheles stephensi, and Culex pipiens). Psychoda alternata larvae were very susceptible, with LC50/LC90 values comparable to those of mosquito larvae (about 10(3)-10(5) spores/ml). The tests with Chaoborus crystallinus larvae showed significant mortality rates at high concentrations, but generally not before 4 or 5 days after treatment. The remaining nontarget organisms did not show any susceptibility. The investigation confirms the specificity of C.b.m. to nematocerous Diptera.
Thirteen strains among 3 species of entomopathogenic bacteria were tested against 3 medically important mosquito species in French Polynesia. Two strains of Bacillus thuringiensis were highly toxic to Aedes polynesiensis, Aedes aegypti, and Culex quinquefasciatus. Six of 7 strains of Bacillus sphaericus tested were highly toxic to Cx. quinquefasciatus but not to the Aedes spp. Clostridium bifermentans serovar. malaysia was more toxic to Ae. polynesiensis than to the other 2 species. Entomopathogenic bacteria merit field testing for larval mosquito control in French Polynesia.
Clostridium bifermentans serovar. malaysia (C.b.m.) is toxic to mosquito larvae. In this study, we quantified its toxicity to the mosquitoes, Aedes aegypti, Ae. albopictus, Ae. caspius, Ae. detritus, Anopheles stephensi, An. gambiae, Culex pipiens and Cx. quinquefasciatus. Anopheles larvae are the most susceptible, followed by Ae. detritus and Ae. caspius, then Culex and other Aedes larvae. According to mosquito species, the LC50 varies from 7 x 10(3) to 1.3 x 10(6) cells/ml. Three concentrations (10(7), 10(6) and 10(5) cells/ml) of C.b.m., Bacillus thuringiensis var. israelensis (B.t.i.) and Bacillus sphaericus were tested on Ae. aegypti, An. stephensi and Cx. pipiens larvae in order to determine the time necessary for each concentration to kill 50 and 90% of the population. Ninety percent of the 3 mosquito populations are killed within 4-15 h by the C.b.m. concentrations. Whatever the concentrations, C.b.m. kills at least 10 times less rapidly than B.t.i. but always quicker than B. sphaericus. Bioassays of C.b.m. bacterial cells or final whole culture were not toxic to Musca domestica and Drosophila melanogaster (Diptera) as well as to Phaedon cochleariae (Coleoptera) and Spodoptera littoralis (Lepidoptera).
The safety of bacterial cells of Clostridium bifermentans serovar malaysia, which is highly toxic to mosquito larvae, was tested on mice, guinea pigs, rabbits, and goldfish. Inoculations of at least 1 x 10(8) cells per animal by routes recommended by World Health Organization (subcutaneous, percutaneous, inhalation, force-feeding, intraperitoneal, intravenous) and tests of subacute toxicity, anaphylactic shock, persistence in heart blood, and virulence by successive passages, were performed on mice, guinea pigs, or both. Growth was monitored for 1 mo before necropsy. Ocular irritation and skin scarification were tested with rabbits. C. bifermentans serovar malaysia did not induce any mortality or abnormal reactions in mammals at a dose 1,000 times higher than the level established by W.H.O. for the demonstration of safety. Bacterial cells are not toxic to goldfish at a dose 1,000 times higher than the LD50 for the target-mosquito larvae. We conclude that C. bifermentans serovar malaysia bacterial cells are safe for laboratory mammals and goldfish.