Biologia e controle microbiano de Urbanus acawoios (Williams, 1926) (Lepidoptera: Hesperiidae): II. patologia e susceptibilidade em larvas infectadas por Bacillus thuringiensis Var. kurstaki (H-3a:3b)

Biology and microbial control of Urbanus acawoios (Williams, 1926) (Lepidoptera: Hesperiidae): II. pathology and susceptibility studies in larvae infected by Bacillus thuringiensis var. kurstaki (H-3a:3b)

Resumos

Devido à falta de informações sobre Urbanus acawoios (Williams, 1926) (Lepidoptera: Hesperiidae), e pelos danos severos por ele causados em árvores de Clitoria racemosa, o presente trabalho foi desenvolvido sob condições de laboratório para verificar a possibilidade de utilizar Bacillus thuringiensis var. kurstaki (H-3a:3b) como agente microbiano para o seu controle. O pH do intestino médio do hesperídeo mostrou ser bastante alcalino, variando de 8,4 a 9,2 (média de 8,7), indicando a possibilidade das larvas serem susceptíveis ao patógeno. Os ensaios confirmaram a alta susceptibilidade a dosagens equivalentes a 110 g / ha, resultando em tempos letais medianos (TL₅₀) de 42,28, 37,18, 28,00 e 51,87 horas para larvas de 3^o, 4°, início e final do 5º ínstares, respectivamente. Três outras dosagens (80, 150 e 280 g/h) foram aplicadas para larvas do 3º ínstar, resultando em TLs50 de 42,62, 30,77 e 30,06 horas, respectivamente. Descrições detalhadas sobre os sintomas externos nas larvas infectadas foram dadas. As alterações histológicas do intestino médio afetado pela d-endotoxina de B. thuringiensis foram descritas. Os resultados obtidos no presente trabalho revelam a grande possibilidade de controlar esta praga utilizando-se produtos e formulados à base desta bactéria.

Bacillus thuringiensis var. kurstaki (H-3a:3b); patologia; Amazônia brasileira; Clitoria racemosa

Due to the lack of information concerning Urbanus acawoios (Williams, 1926) (Lepidoptera: Hesperiidae), and the severe damage caused by it in Clitoria racemosa trees in Manaus, AM, the present research was conducted. The study was undertaken under laboratory conditions, in order to investigate the possibility of its microbial control, utilizing a commercial formulation, Dipel, based on Bacillus thuringiensis var. kurstaki (H-3a:3b). The larval mid-gut contents of this insect species showed to be highly alkaline, with a pH varying between 8.4 and 9.2, with an average of 8.7, indicating initially, a possible susceptibility of the larval stage to such a pathogen. Posteriorly, Such an indication, was confirmed by bioassays. During the preliminary tests, a dosage, equivalent to 110 g / ha (17.40 IU/cm² of leaf-covered area) was utilized and resulted in median lethal times (LTs₅₀) of 42.28, 37.18, 28.00 and 51.87 hours for the 3^rd, 4^th, beginning of the 5^th and end of the 5^th instar, respectively. Giving more attention for the 3^rd instar larvae, three dosages were applied: 80 g/ha (13 IU/cm²), 150 (25 IU/cm²) and 280 g/ha (45 IU/cm²). In this case, the LTs₅₀ were calculated as 42.62, 30.77 and 30.06 hours, for each dose, respectively. External symptoms of the bacterial disease were studied among 5^th instar infected larvae. Detailed description of these symptoms is given. The mid-gut histopathological changes caused by the d-endotoxin of B. thuringiensis are also described. The results obtained during the present work could indicate applications of B. thuringiensis, as a promising method for the microbial control of this urban pest.

Brazilian Amazon; Bacillus thuringiensis var. kurstaki (H-3a:3b); pathology; Clitoria racemosa

Datas de Publicação

• Publicação nesta coleção
  Dez 2001