Experimental observation of toxic effect of Bacillus thuringiensis var. israelen-sis against Aedes,Culex and Anopheles larvae / 中国血吸虫病防治杂志

Objective To evaluate the toxic effect of Bacillus thuringiensis var. israelensis(Bti)wettable powder against Ae-des,Culex and Anopheles larvae. Methods The biological assay was applied to test the lethal concentration of 50%(LC50)of Bti wettable powder against Aedes,Culex and Anopheles larvae. Results The LC50(s) of Bti wettable powder against Aedes albopictus, Culex pipiens pallens and Anopheles sinensis larvae were 0.104,0.160μg/ml and 0.324μg/ml,respectively;its biological poten-cies against them were 0.125,0.192 IU/ml and 0.389 IU/ml,respectively. The LC50(s) of continuous contact of Bti wettable powder with An. sinensis stageⅢlarvae for 1,2 d and 3 d were 0.324,0.092μg/ml and 0.032μg/ml,respectively,and its biological po-tencies were 0.389,0.110 IU/ml and 0.038 IU/ml,respectively. The LC50(s) of the bacteria against An. sinensis stageⅠ,Ⅱ,Ⅲ,Ⅳwere 0.024,0.137,0.324 μg/ml and 0.450 μg/ml,respectively,and the biological potencies were 0.029,0.164,0.389 IU/ml and 0.540 IU/ml,respectively. Conclusion Bti wettable powder has a good toxicity to Aedes,Culex and Anopheles larvae,espe-cially for the latter two. It is better to apply the bacteria at the early stage of mosquito larvae.

Production of bio-inseticide Bacillus thuringiensis var. israelensis in semicontinuous processes combined with batch processes for sporulation

The aim of this work was to study the production of the bioinsecticide using the aerobic cultivation. Two-stage cultivation process was used: aerobic vegetative growth and end-phase of sporulation (with aeration and without aeration). The cuts of working volume evaluated were 20, 40, 60 and 80 percent. The highest value of spore concentration (2.17x10(9) CFU/mL) and spore productivity (7.2x10(7) CFU/mL.h) were observed using SP60. The lethal concentration (CL50) obtained through the aeration process and non-aeration process were 0.21 and 0.05 mg/L, respectively. The specific potential of the bioinsecticide produced without aeration (0.025 mg/10-12 CFU) was two times higher than that obtained with aeration (0.05 mg/10-12 CFU).

Development of a Low Cost Bioprocess for Endotoxin Production by Bacillus thuringiensis var israelensis Intended for Biological Control of Aedes aegypti

Aedes aegypti is the vector of Dengue disease, responsible for 20,000 deaths/year worldwide. Bacillus thuringiensis var israelensis - Bti releases selective and effective toxins (crystal proteins) against A. aegypti larvae. We present a low cost bioprocess for toxin production, accomplished by a selected Brazilian strain Bti (BR-LPB01) and employment of low cost substrates. Soybean meal and sugarcane molasses lead to high toxic effectiveness after 2L bioreactor fermentation (LD50=26ng/mL), near to the reference strain IPS82 (LD50=17.3 ng/mL). The pH ranged between 5.8 and 7.0 during the exponential growth period and between 7.0 and 8.4 during the stationary phase, with low activity. Thus, control of foam and pH 7.0 were started and proved to be crucial for high activity. It was verified that the fermentation could be discontinued after 20 hours, when the highest activity was present.

A dengue é transmitida pelo Aedes aegypti, doença responsável por 20.000 mortes/ano no mundo. Bacillus thuringiensis var israelensis libera toxinas seletivas e eficazes (proteínas cristal) contra larvas de A. aegypti. Propõe-se um bioprocesso de baixo custo para a produção da toxina, pelo emprego de uma cepa brasileira selecionada de Bti (BR-LPB01) e de substratos de baixo custo. Farelo de soja e melaço de cana levaram a eficácia tóxica alta após fermentação em biorreator 2L (DL50=26ng/mL), valor próximo a estirpe de referência IPS82 (DL50=17,3 ng/mL). O pH variou entre 5,8 e 7,0 durante o período de crescimento exponencial e entre 7,0 e 8,4 durante a fase estacionária, com baixa atividade larvicida. Assim, controles de espuma e de pH 7,0 foram iniciados e demonstraram serem cruciais para alta atividade. Verificou-se que a fermentação deve ser interrompida após vinte horas, quando se obtém a maior atividade.

Investigação da genotoxicidade de larvicidas biológicos e sínteticos utilizados para o controle de Aedes aegypti / Genotoxicity investigation of biologic and synthetic larvicide utilized for the control of Aedes aegypti

A dengue é atualmente considerada a mais importante arbovirose que afeta o homem. O agravamento desta situação epidemiológica tem acarretado um aumento expressivo no uso de inseticidas organofosforados no combate ao vetor, principalmente o temefós, que é amplamente e sistematicamente aplicado em ambientes urbanos em reservatórios de água, até para o consumo humano. Este projeto propôs investigar efeito genotóxico (clastogênico) em células de mamíferos, induzido pela exposição ao temefós (grau técnico 95,5%), e ao biolarvicida Bacillus thuringiensis sorovar israelenses (Bti) - IPS 82, ambos empregados no controle do Aedes aegypti. Na avaliação genotóxica foram utilizadas células da medula óssea de camundongos albinos Swiss Webster de ambos os sexos, empregando-se os testes de metáfase e de micronúcleos para detecção dos danos cromossômicos: aberrações cromossômicas e micronúcleos. Os camundongos foram tratados com temefós (grau técnico 95,5%) nas concentrações de 27,75; 55,5 e 111 mg/kg ou com água destilada 10 ml/kg, via gavagem, como controle negativo ou com Ciclofosfamida a 25 mg/kg, via i.p., como controle positivo por 24, 48 e 72h, em dose única ou em 9 doses repetidas (1 dose/semana). Outros grupos foram tratados com Bti nas doses de 204 e 122,4 UFC (Unidade Formadora de Colônia) ou água destilada (200 ?l) como controle negativo, via gavagem, por 24 e 48h. Os resultados observados confirmaram a ação genotóxica induzida pelo inseticida temefós em camundongos de ambos os sexos, com a formação de micronúcleo em eritrócitos policromáticos (PCE MN), em todas as concentrações testadas 24h após o tratamento único. Na concentração de 111,00 mg/kg induziu PCE MN também após 48 e 72h em dose única e após tratamento com 9 doses. O temefós induziu também aberrações cromossômicas nas células em metáfases, em todas as concentrações testadas, 24h após tratamento único, e na concentração de 111,00 mg/kg, também após 48 e 72h de tratamento...

Developing new approaches for detecting and preventing Aedes aegypti population outbreaks: basis for surveillance, alert and control system

A new approach to dengue vector surveillance based on permanent egg-collection using a modified ovitrap and Bacillus thuringiensis israelensis(Bti) was evaluated in different urban landscapes in Recife, Northeast Brazil. From April 2004 to April 2005, 13 egg-collection cycles of four weeks were carried out. Geo-referenced ovitraps containing grass infusion, Bti and three paddles were placed at fixed sampling stations distributed over five selected sites. Continuous egg-collections yielded more than four million eggs laid into 464 sentinel-ovitraps over one year. The overall positive ovitrap index was 98.5 percent (over 5,616 trap observations). The egg density index ranged from 100 to 2,500 eggs per trap-cycle, indicating a wide spread and high density of Aedes aegypti (Diptera: Culicidae) breeding populations in all sites. Fluctuations in population density over time were observed, particularly a marked increase from January on, or later, according to site. Massive egg-collection carried out at one of the sites prevented such a population outbreak. At intra-site level, egg counts made it possible to identify spots where the vector population is consistently concentrated over the time, pinpointing areas that should be considered high priority for control activities. The results indicate that these could be promising strategies for detecting and preventing Ae. aegypti population outbreaks.