Laboratory studies of the microsporidian Plistophora culicis (Weiser) infecting Culex pipiens fatigans Wied

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Abstract
Populations of Culex pipiens fatigans Wied. were exposed to infection by Plistophora culicis (Weiser) by allowing eggs to hatch in water containing a known concentration of spores. At 26°C–28°C (mean 27°C) exposure of newly hatched larvae to a concentration of 6 000 spores/ml resulted in a 12–9% reduction in the net reproduction rate, and exposure to a concentration of 12 000 spores/ml to a reduction of 24·0%. These reductions were due to an increase in the rate of female mortality and an increase in the number of eggs laid which were non-embryonated and hence did not hatch. At 33°C–35°C (mean 34°C), although the spores of the microsporidian were not killed, development of P. culicis in the mosquito was inhibited. At 19·5°C–20·5°C (mean 20°C), the net reproduction rate of a population exposed as newly hatched larvae to a concentration of 1 890 spores/ml was reduced by 35·6%, due to a greatly increased rate of female mortality. P. culicis, with the inocula tested, is not considered of practical use against C.p. fatigans; more infective spore inocula are not feasible with the present methods of propagating the parasite.