Effects of Polydispyrenia simulii (Microspora; Duboscqiidae) on Development of the Gonads of Simulium pertinax (Diptera; Simuliidae)

Abstract

Microsporidial infections of insects are often chronic and nonlethal in nature. Consequently, epizootics of these pathogens do not usually result in dramatic suppression of host populations. Rather, such pathogens exert sublethal effects on their hosts such as reduced fecundity, shortened longevity and a general loss of vigor.Medically important insects and agricultural pests have been investigated for a long time with regard to sublethal effects caused by microsporidiosis (Gaugler & Brooks 1975, Andreadis & Hall 1979, Andreadis 1983, 1985, Sweeney et al. 1989, Lockwood & Debrey 1990, Castello Branco Jr 1998. Blackflies represent an important family among the medically important insects due to their role as vectors of human and animal helminthiasis and because the nuisance caused by their biting habit (Crosskey 1990). Simulium pertinax Kollar is the most antropophilic species occurring in southeastern Brazil and is the main target of government and other control programmes in these areas.Although microsporidia are considered the most common and worldwide blackfly pathogen, their ecology and epizootiology are poorly known in this host group. The aim of this work is to evaluate the effects of the infection caused by the microsporidium Polydispyrenia simulii in the gonads of both sexes of the blackfly S. pertinax reared from heavily infected larvae. MATERIALS AND METHODSLarvae of S. pertinax were collected from their natural breeding sites and kept in a laboratory rearing system adapted from Raybould and Grunewald (1975) (Fig.). Separate rearing systems were stocked with blackfly larvae infected and not-infected with P. simulii. Adults of both sexes originating from healthy and infected larvae were obtained from the system and then transfered to glass holding chambers of 0.29 m³. The rearing system and the chambers were maintained at room temperature without photoperiod control. The adults originated from healthy and infected larvae were kept separate.Human bait (nude forearm) was offered to the female flies twice a day (40 min each one). Filter paper bands soaked in 20% sucrose solution were also provided for the adults to feed. After blood feeding, each S. pertinax female was maintained in glass vials of 40 ml containing filter paper bands soaked with sucrose solution.S. pertinax males and females were dissected in 0.85% saline solution at regular intervals. Females were dissected after the seventh day from the first blood meal while males were dissected after the fourth day from the adult fly emergence. The testes and ovaries were examined under the microscope (100x up to 1,000x). The motility of