A new black fly isolate of Bacillus thuringiensis autoagglutinating strain highly toxic to Simulium pertinax (Kollar) (Diptera, Simuliidae) larvae

Abstract

Formulations containing the entomopathogenic Bacillus thuringiensis serovar israelensis strain Bacillus thuringiensis is a Gram-positive, spore-forming bacterium which produces a parasporal body during sporulation. The proteins contained in the parasporal crystal (delta-endotoxins) are specific insect gut toxins which have no significant effect on non-target organisms (Siegel 2001). The mode of action after ingestion involves solubilization of the protein in the alkaline conditions of the insect midgut, followed by activation of the protoxin into toxin through cleavage of specific regions by gut proteases. Then, the so called toxin binds to specific receptors in the brush border membrane vesicles of the midgut columnar cells. The binding is a two-step process, the second part being the insertion of the toxin into the cell membrane leading to pore formation, osmotic imbalance, disruption of the cell membrane and finally, death of the insect (Van Rie et al. 1990, Knowles 1994.The use of bioinsecticides based on B. thuringiensis to control insects from the orders Diptera, Coleoptera, and Lepidoptera and more recently against Hymenoptera, Orthoptera, and Mallophaga, has stimulated the search for other natural pathogens (Schenpf et al. 1998 Between 1995 to 1998, an isolation program was set up to obtain entomopathogenic Bacillus from Simulium larvae and adults in the Southeast region of Brazil. Eighteen strains of B. thuringiensis and one of B. sphaericus were isolated (Cavados et al. 2001). Preliminary bioassays were performed and one of the B. thuringiensis strains (LFB-FIOCRUZ 1035) showed promising activity against Aedes aegypti and Culex quinquefasciatus (Cavados et al. 2001).In the present study, the toxicity of the autoagglutinating strain LFB-FIOCRUZ 1035 was evaluated against two Dipteran species, S. pertinax and Ae. aegypti larvae, and compared with a standard powder formulation of the reference B. thuringiensis serovar israelensis strain IPS-82, which is used in commercially available bioinsecticides. MATERIALS AND METHODSBacterial strains -Two strains of B. thuringiensis were used, one of them IPS-82 (LFB-FIOCRUZ 584) serotype H-14, isolated from the standard powder prepared by the Pasteur Institute of Paris, and the other LFB-FIOCRUZ 1035, an autoagglutinating strain isolated from S. pertinax larvae collected in a natural breeding-site in Growth started with a pre-inoculum to reduce the duration of the lag phase of bacterial growth. After inoculation in 125 ml Erlenmeyer flasks containing 50 ml of the medium, the flasks were incubated in a New Brunswick Scientific agitator series 25D, at 175 opm and 30°C for 6 h. Subsequently, 3 ml were transferred to 500 ml Erlenmeyer flasks containing 150 ml of the soy flour and inorganic salts medium and incubated as previously described for a further 72 h period.Once sporulation had reached 95% of free spores and crystals, each culture was centrifuged (6000 g, 10°C), the supernatant removed and the remaining material was kept in an amber container with the pH adjus...

Bacillus thuringiensis isolates entomopathogenic for Culex quinquefasciatus (Diptera: Culicidae) and Anticarsia gemmatalis (Lepidoptera: Noctuidae)

“…Isolate ID-MD4, obtained from M. domestica, showed the same percentage mortality against C. quinquefasciatus as the reference strain IPS-82. Similar observations were reported by Cavados et al (2005), who reported that bioassays of a B. thuringiensis isolate obtained from the black fly Simulium pertinax, which had been captured in a field in southeastern Brazil, was not only effective against S. pertinax but also had comparable toxicity against the important disease vector Aedes aegypti as reference strain IPS-82 which is only effective against mosquitoes.…”

“…The search for new B. thuringiensis isolates and their characterisation has been carried out by several research groups in different countries (Dias et al, 1999;Uribe et al, 2003;Cavados et al, 2005;Jara et al, 2006), these isolates being important in the control of insects because they represent new alternatives in integrated pest management (IPM). The majority of natural B. thuringiensis isolates with insecticidal activity are effective against lepidoptera larva (Alves et al, 1998), with B. thuringiensis strains active against diptera or coleoptera being more difficult to isolate (Mohammedi et al, 2006;Armengol et al, 2007).…”

Phenotypic and genotypic features of new autoagglutinating Bacillus thuringiensis strains

“…In the biological activity assays against Ae. aegypti larvae, the strains these groups demonstrated they can be more effective against insects vectors than the strain currently used in programs to control of Dipteran vectors (Cavados et al, 2005). Such proteins may represent new unknown cry genes, but analysis of the genes that encode this toxin is required to understand the function of each of these polypeptides in larvicidal activity.…”

“…The autoagglutinating B. thuringiensis strains (LFB-FIOCRUZ 969, 1038 and 1043) and the B. thuringiensis serovar israelensis IPS-82 (LFB-FIOCRUZ 584), were growth in a fermentation medium based on soy flour and inorganic salts (such as MgSO 4 , MnSO 4 , FeSO 4 , ZnSO 4 , CaCl 2 ) developed in the Laborató rio de Fisiologia Bacteriana, IOC-FIOCRUZ (Cavados et al, 2005).…”

Desenvolvimento de nova metodologia para aplicação de bioinseticidas no controle de borrachudos (Diptera: Simuliidae) em ribeirões com fluxo de água irregular

“…Bacillus thuringiensis israelensis Berliner (B.t.i.) tem sido utilizada como princípio ativo de bioinseticida por sua patogenicidade e especificidade sobre larvas de borrachudos (LACEy;LACEy, 1981;BECkEr et al, 1992;BrOwN et al, 1998;2000;rODriGUES;wANDErLi;JOSé, 1998;NAyAr et al,1999;ChUNG et al, 2001;FiLLiNGEr;kNOLS;BECkEr, 2003;POLLOm, 2003;CAVADOS et al, 2005).…”