Influence of temperature on microsporidia infections in a natural population of Simulium pertinax Kollar, 1832 (Diptera; Simuliidae)

During the studies involving the correlation between the water temperature of the breeding site of Simulium pertinax larvae and the infection prevalence by microsporidia, developed in the Andorinhas river, Magé, RJ, weekly samples of blackfly larvae were taken within a two-year period (2001-2002 and 2003-2004), and it was noticed that the infections by Amblyospora sp. were more prevalent when compared to infections by Polydispyrenia sp. in larvae. It was also observed that the infections do not follow the same pattern, since the genus Amblyospora was recorded almost every month during the study with the exception of December, 2001. In the results of correlation between the environmental water temperature and the microsporidia infection rates, it was observed that for the first period studied, there was a high negative correlation, while during the second period there was absence correlation. On the other hand, the Amblyospora sp. infection rates prove that the correlation was high and significant in the first period, but was not significant in the second sampling period and Polydispyrenia sp. showed absence correlation in both periods.

Este estudo envolvendo a correlação entre a temperatura da água do criadouro de larvas de Simulium pertinax e a prevalência de infecção por microsporídeos, foi desenvolvido no rio Andorinhas, Magé, RJ, onde foram realizadas coletas semanais de larvas de simulídeos no período de dois anos (2001-2002 e 2003-2004), e foi observado que as infecções por Amblyospora sp. apresentaram maior prevalência quando comparadas com as infecções por Polydispyrenia sp. Com isso, verificou-se que as infecções não seguem o mesmo padrão, onde o gênero Amblyospora foi relatado em quase todos os meses de desenvolvimento do estudo, com exceção apenas de dezembro de 2001. Nos resultados de correlação entre a temperatura ambiente e a taxa de infecção por microsporídeos no primeiro período de estudo, foi observada uma forte correlação negativa, porém foi verificada ausência de correlação no segundo período. Embora tenha sido evidenciada uma forte e significante correlação com a taxa de infecção por Amblyospora sp. no primeiro período, esta correlação mostrou-se não significativa no segundo período de amostragem e Polydispyrenia sp. apresentou ausência de correlação em ambos os períodos de estudo.

Histopathological and ultrastructural effects of delta-endotoxins of Bacillus thuringiensis serovar israelensis in the midgut of Simulium pertinax larvae (Diptera, Simuliidae)

The bacterium Bacillus thuringiensis (Bt) produces parasporal crystals containing delta-endotoxins responsible for selective insecticidal activity on larvae. Upon ingestion, these crystals are solubilized in the midgut lumen and converted into active toxins that bind to receptors present on the microvilli causing serious damage to the epithelial columnar cells. We investigated the effect of these endotoxins on larvae of the Simulium pertinax, a common black fly in Brazil, using several concentrations during 4 h of the serovar israelensis strain IPS-82 (LFB-FIOCRUZ 584), serotype H-14 type strain of the Institute Pasteur, Paris. Light and electron microscope observations revealed, by time and endotoxin concentration, increasing damages of the larvae midgut epithelium. The most characteristic effects were midgut columnar cell vacuolization, microvilli damages, epithelium cell contents passing into the midgut lumen and finally the cell death. This article is the first report of the histopathological effects of the Bti endotoxins in the midgut of S. pertinax larvae and the data obtained may contribute to a better understanding of the mode of action of this bacterial strain used as bioinsecticide against black fly larvae.