Predicting occurrence of the fungal symbiote Harpella colonizing black fly larvae in coastal streams of Alabama and Mississippi, USA.

The environmental conditions governing symbioses are poorly known in aquatic systems. Stream conditions associated with the distribution of the black fly (Simuliidae) midgut symbiote Harpella were investigated in southern Alabama and Mississippi streams. Stream conditions that were most useful in predicting the distribution of Harpella spp. in the study area were dissolved oxygen and water temperature. Presence of Harpella species in streams was associated with higher dissolved oxygen and decreased water temperature compared to streams where Harpella spp. was absent. Stream conditions associated with the distribution of Harpella spp. in other regions of the world vary according to conditions other than those elucidated here, indicating that geography, host species, and stream conditions play important roles in the spatial distribution of Harpella species.