Seasonality and prevalence rates of microsporidia in Simulium pertinax (Diptera : Simuliidae) larvae in the region of Serra dos Órgãos, Rio de Janeiro, Brasil

A major means of fighting arthropod-borne diseases is control of the vector species. Successful vector control began in the 1940s with the synthesis of the first organochloride (DDT), and has continued with compounds such as organophosphates, carbamates, and pyrethroids (Margalit and Dean, 1985). Chemical insecticides have been effective and economical due to their broad spectrum of action and long residual effects. However, resistance to these pesticides in vector species, as well as harmful environmental effects has led to increased research into efficient and environmentally friendly control methods (Zahner et al., 1993). Biological control provides agents with greater specificity for vector species with fewer negative environmental consequences. For the Simuliidae, the shift from chemical to biological control began in the 1980s with the use of Bacillus thuringiensis serovar israelensis (BTI). In Brazil, the first program for black fly control with BTI began in 1989 in S~ao Paulo state. This program has been successful but expensive (Ara ujo-Coutinho, 1995); therefore, despite good results with BTI, efforts continue to discover natural pathogens in Brazilian simuliid species as alternative or complementary control methods of equal effectiveness. Microsporidia are common pathogens of black flies, but species diversity and seasonal occurrence are poorly known in most localities and mechanisms for transmission are unknown (Lacey and Undeen, 1986). Simulium pertinax is the most common and widely distributed black fly species in southwest