Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Vector competence studies evaluated the roles of Aedes trivittatus, Culex tarsalis, and Culex spp. (Cx. pipiens, Cx. restuans, and Cx. salinarius) in the transmission cycle of western equine encephalomyelitis (WEE) virus in Iowa. Oral and parenteral susceptibilities of these mosquitoes were compared for three strains (7738, 7746, and Fleming) of WEE virus. Aedes trivittatus and Cx. tarsalis were much more susceptible than Cx. restuans and Cx. pipiens to WEE virus, whether infected orally or parenterally, and Cx. salinarius was refractory. The susceptibility of these species varied with the strain of virus tested. Older, late season Culex spp. were less susceptible than young, early season Culex. Culex tarsalis was most efficient in the transmission of WEE virus to chicks, but 44% of the Aedes tested also transmitted virus. Only a few infected Culex spp. fed on chicks, but those that did transmitted virus. Differences were observed in the ability of Ae. trivittatus, Cx. tarsalis, and Cx. pipiens to transmit three strains of virus;Three genotypes (GHA, 19, and S1) of White Leghorn chicks were tested for susceptibility to needle-inoculated WEE virus. Chicks were highly susceptible and more sensitive than mice to infection with virus strains 7738 and 7746. Five haplotypes (B('1)H-B('19)L, B('1)L-B('19)H, B('2)-B('2), B('1)-B('1)L, and B('1)-B('1)H) of genotype S1 were less sensitive than mice to the Fleming strain. B('1)-B('1)H had the lowest susceptibility to infection with WEE virus. No profound differences in LD(,50)'s among the three genotypes were determined, but the virulence of strains 7738 and 7746 were significantly different. Genotype GHA was highly sensitive to mosquito-inoculated WEE virus;Arbovirus surveillance activities indicated that Cx. tarsalis is the primary vector of St. Louis encephalitis (SLE) and WEE viruses in Iowa. High populations of Culex spp. contribute to SLE virus amplification, and Ae. trivittatus is important in the natural maintenance of WEE virus in Iowa. From 1978 through 1980, numerous isolations of Flanders (FLA) and trivittatus (TVT) viruses were made from five species of mosquitoes, and LaCrosse (LAC) virus was isolated from Ae. triseriatus. Forty out of 2,298 wild birds tested for hemagglutination-inhibition (HI) antibodies against SLE and WEE viruses had antibodies to WEE, and ten had SLE antibodies. A sentinel chicken flock seroconverted (WEE) in 1979.



Digital Repository @ Iowa State University,

Copyright Owner

Richard Graham Andre



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128 pages

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Entomology Commons