Attraction of Culex pipiens to uropygial gland secretions does not explain feeding preference for American robins

Culex pipiens, the endemic mosquito vector of West Nile virus in eastern North America, is responsible for maintenance of the virus in avian reservoir hosts, the most important of which appears to be the American robin. One reason for the greater involvement of robins is believed to be the feeding preference of Cx. pipiens, however, the basis of this preference is not understood. We tested the hypothesis that the species-specific chemical profile of avian uropygial gland secretions are used by Cx. pipiens as cues to locate birds and, therefore, may contribute to the observed feeding preferences. We used gas chromatography-mass spectrometry to identify the semi-volatile components of the uropygial gland secretions of American robins and two other common reservoir host species, the house sparrow and European starling. We found that the chemical composition of the robin secretions was different from those of the sparrows and starlings. Through behavioral choice trials conducted in a dual-port olfactometer, we also found that Cx. pipiens did not prefer the secretions of robins over the other two species. Surprisingly, however, we found that Cx pipiens were more often attracted to live starlings over robins and to the secretions of starlings over those of robins.