COMPARATIVE SUSCEPTIBILITY OF INTRODUCED FOREST-DWELLING MOSQUITOES IN HAWAI'I TO AVIAN MALARIA, PLASMODIUM RELICTUM

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Abstract
To identify potential vectors of avian malaria in Hawaiian native forests, the innate susceptibility of Aedes albopictus, Wyeomyia mitchellii, and Culex quinquefasciatus from 3 geographical sites along an altitudinal gradient was evaluated using local isolates of Plasmodium relictum. Mosquitoes were dissected 5-8 and 9-13 days postinfective blood meal and microscopically examined for oocysts and salivary-gland sporozoites. Sporogony was completed in all 3 species, but prevalence between species varied significantly. Oocysts were detected in 1-2% and sporozoites in 1-7% of Aedes albopictus that fed on infected ducklings. Wyeomyia mitchellii was slightly more susceptible, with 7-19% and 7% infected with oocysts and sporozoites, respectively. In both species, the median oocyst number was 5 or below. This is only the second Wyeomyia species reported to support development of a malarial parasite. Conversely, Culex quinquefasciatus from all 3 sites proved very susceptible. Prevalence of oocysts and sporozoites consistently exceeded 70%, regardless of gametocytemia or origin of the P. relictum isolate. In trials for which a maximum 200 oocysts were recorded, the median number of oocysts ranged from 144 to 200. It was concluded that Culex quinquefasciatus is the primary vector of avian malaria in Hawai'i.