MEIOSIS IN THE MALE OF CULEX PIPIENS AND AEDES ALBOPICTUS AND FERTILIZATION IN THE CULEX PIPIENS-COMPLEX

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Abstract
As a result of close somatic pairing of the chromosomes visible leptotene stages do not occur in either Culex pipiens or Aedes albopictus. Bouquet stages were not observed during early meiotic prophase. The sperm of C. pipiens consist of a head 14 μ long and a tail 200 μ long. More than 80% of sperm treated with 3H-Tdr could be sufficiently labeled by feeding fourth instar larvae 10 μCi/ml/larva 3H-Tdr for about 3 days. An almost complete label could be found in the sperm head and only some few grains in the DNA of the mitochondrial bodies of the tail.In the C. pipiens female, meiosis is activated by the entrance of the sperm and karyogamy is effected about 50 minutes after oviposition. During the meiotic divisions the sperm moves to the center of the egg and fuses with the pronucleus. If supernumerary sperm are present they most often are found near the micropylar pole of the egg.Although the frequency of polyspermy is low, one or two sperm are usually present in the fertilized eggs.In incompatible crosses with strains of different geographical origins (♂ Hamburg ♀ Paris) the egg is activated by the sperm and the meiotic divisions begin but the sperm does not succeed in fusing with the pronucleus. The developing embryos are haploid and embryogenesis leads to irregular differentiation; 99.9% of the embryos die. Apparently reactions between sperm and egg cytoplasm prevent karyogamy. The different models of cross-reactions in the C. pipiens-complex are discussed; mitochondrial DNA is suggested to be involved in fertilization.

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