Vector roles of Fennoscandian mosquitoes attracted to mammals, birds and frogs.

1. Mosquitoes were sampled with five suction traps, from May to October 1983, at a forest site in south-central Sweden. 2. Twenty-three species of mosquitoes were identified among the total of 3108 females collected: 4% of them in an unbaited trap, 3% in a trap baited with two frogs, 24% with a guinea-pig, 28% with a hen and 40% in a trap baited with a rabbit. 3. The dominant species of Culicidae trapped were 39% Aedes communis (De Geer), 21% Ae. cinereus Meigen, 14% Coquillettidia richiardii (Ficalbi), 8% Ae. punctor (Kirby) and 4% Culiseta morsitans (Theobald). 4. Aedes annulipes (Meigen), Ae. cantans (Meigen), Ae. cinereus, Ae. communis and Ae. punctor were mostly attracted to the rabbit, whereas Culiseta morsitans, Culex pipiens L. and/or Cx torrentium Martini were strongly ornithophilic. 5. Based on these and previously published data the ecological and behavioural potential of the mosquitoes to transmit Sindbis, Inkoo, Tahyna and Batai viruses, tularaemia (caused by Francisella tularensis) and Ixodes-borne borreliosis (caused by Borrelia burgdorferi) in Fennoscandia is discussed. 6. The data support the hypothesis that Sindbis virus, which is enzootic in bird populations in Fennoscandia, is vectored between birds by Cx pipiens/torrentium and Cs. morsitans, and that abundant Aedes spp., particularly Ae. cinereus, which feed on both birds and mammals, are primary link vectors from infective birds to man and other mammals.