SUSTAINED EFFECTS OF LARVAL BLACKFLY SETTLEMENT ON FURTHER SUBSTRATE COLONIZERS

Artificial substrates and histological staining procedures have been u sed to study interference effects among blackfly larvae. Colonising la rvae apply silk to the substratum to attach themselves for filter feed ing, locomotion or pupation. We have hypothesised that species might r eact differently to alterations of the substratum caused by the silk o f previously colonisers and have therefore compared Simulium noelleri FRIEDERICHS and Simulium vernum MACQUART, which are characteristic of different habitats. The number of larval colonisers and the number and position of their silk pads on previously colonised and new control s ubstrates were recorded after 24 h of exposure in streams. The results support our hypothesis that blackfly species react to surface propert ies differently and are thus affected differently by previous colonise rs. Whereas S. noelleri seems to prefer previously colonised substrate s or, at least, is not negatively affected by silk remnants on the sur faces, S. vernum appears to avoid areas covered by the silk of other l arvae. We conclude that interference caused by silk remnants and speci es-specific differences in tolerance concerning surface properties aff ect simuliid density, distribution and colonisation dynamics.