Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


An analysis of the cytoplasmic incompatibility system in Culex pipiens has been made. Both normal and antibiotic-resistant strains have been established using erythromycin, chloramphenicol and tetracycline. A complete genetic analysis has been made using all possible reciprocal crosses. Crosses between the normal strains show unidirectional compatibility. The genetic crosses involving the tetracycline-resistant strain show a reversal of the direction of compatibility when compared with those involving the untreated parental strain. Erythromycin and chloramphenicol-resistant strains exhibited no such change in direction of compatibility when compared with their respective untreated parental strains. Exceptional crossing relationships between chloramphenicol and tetracycline-resistant strains were found. The presence of presumptive rickettsia-like endosymbiotes was observed both before and after rigorous treatments of normal laboratory strains with the above antibiotics. Agarose gel electrophoresis of mitochondrial DNA following digestion with restriction endonucleases Hae III and Hinf I demonstrated a clear heterogeneity of base sequences between unilaterally incompatible strains. No differences in base sequences of the mtDNAs were detected between the chloramphenicol-resistant strain from its normal parental strain following digestion with seven different endonuclease systems. Evidence obtained from electron microscopy of mosquito ovarian tissue in this investigation does not confirm the hypothesis that rickettsia-like endosymbiotes are the etiological agent of cytoplasmic incompatibility in Culex pipiens. Differences in nucleotide sequences of mtDNAs between cytoplasmically incompatible strains of Culex pipiens were found to be consistent with results obtained in many other cytoplasmic systems. Further evaluation of the involvement of mtDNA in cytoplasmic incompatibility of Culex pipiens is appropriate.