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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)

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 3rd, 4th, beginning of the 5th and end of the 5th instar, respectively. Giving more attention for the 3rd 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 5th 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

Instituto Nacional de Pesquisas da Amazônia Av. André Araujo, 2936 Aleixo, 69060-001 Manaus AM Brasil, Tel.: +55 92 3643-3030, Fax: +55 92 643-3223 - Manaus - AM - Brazil