The effects of Nosema algerae Vavra and undeen (Microsporida: Nosematidae) pathogen of Culex pipiens L.(Diptera: Culicidae) from Egypt on fecundity and longevity of the host.
A microsporidian, Nosema algerae Vavra and undeen, was found parasitizing larvae and adults of a laboratory colony of Culex pipiens L. originated from Gharbia Governorate. A detailed examination of the developmental stages of the pathogen under light and electron microscopes showed that they are typical of the original characteristics of N. algerae. Other observations on the infected individuals revealed that spores of the pathogen were found in all organs of the infected mosquitoes except the nervous system. The most heavily infected organ was the alimentary canal, particularly the mid gut. The susceptibility of the different larval instars of a laboratory maintained Cx. pipiens colony to infection by N. algerae was determined. Using 24 hours exposure to a range of doses between 40 and 5 x 10(5) spores per cm, larvae of the 1st and 2nd instars were more susceptible to infection than 3rd and 4th instar larvae as indicated by the differences in the estimated IC50 dosages. The dosages of N. algerae which produced 50% mortality (LC50) in each group of treated larvae was approximately 25-30 times higher than the doses that caused 50% infection. When a sublethal dose of 1.2 x 10(3) spores per cm2 of N. algerae was used to induce infection in each of the different larval instars infection rates of 100% were obtained in all exposed larval instars and in adults developed from them. Females from larvae infected with N. algerae had significantly reduced fecundity, fertility, and longevity regardless the larval instar in which infection was initiated. However, the reduction was obviously high when 1st and 2nd instars were exposed. The accumulative effects of reduced survival and fecundity on the reproductive potential of the infected females derived from larvae that were infected as 1st and 2nd instars probably serve to limit the natural increase of mosquito populations. Further studies are necessary, however, to determine the efficacy of this pathogen on target species in the natural environment where the combined effect of the pathogen and environmental stresses may enhance its pathogenicity.
Seif
A I
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Department of Zoology, Faculty of Science, Tanta University, Egypt.
D000818:Animals; D003465:Culex / Q000469:parasitology* / Q000502:physiology*; D004534:Egypt; D005298:Fertility; D006790:Host-Parasite Interactions; D008136:Longevity; D016818:Nosema