Ratio changes in blood-feeding and voltinism in black flies (Diptera: Simuliidae) over a latitudinal gradient in North America north of Mexico

We explored how the ratio of blood-feeding behaviour—nonfeeding, bird feeding (ornithophily) and mammal feeding (mammalophily)—and voltinism (univoltine and multivoltine) vary over a latitudinal gradient from Alaska to Florida. These two fixed species traits were divided into five mutually exclusive combinations of trait states—nonfeeding/univoltine, ornithophilic/univoltine, mammalophilic/univoltine, ornithophilic/multivoltine and mammalophilic/multivoltine—within each of three datasets (north, east and west). We found a significant association between location (north, east and west) and trait state, which was driven by the large percentage of nonfeeding females in the north. When this trait state was removed, no significant differences were found for the remaining trait states and locations. Although the distribution of trait states did not differ between east and west datasets, the distribution with relation to 1° changes in latitude within each of these datasets showed distinct differences. In the east, both ornithophilic/univoltine and mammalophilic/univoltine species significantly increased with latitude, in proportion to the total species present. In contrast, the proportion of mammalophilic/multivoltine species decreased as latitude increased. Ornithophilic/multivoltine species in the east and the trait states in the west did not show any significant relationship to latitude.