An ecological classification of primary labral fans of filter-feeding black fly (Diptera: Simuliidae) larvae

Abstract

A conceptual model that uses labral-fan structure to predict the distribution of black fly species within a catchment is proposed. The model is based on water flow, seston availability, and the structure of the primary labral fans of mature black fly larvae from southern Africa. The model predicts that black fly larvae found in fast-flowing (>1.0 m/s) seston-rich (>50 mg/L) water will tend to have strong fans with a porous ray structure, whereas larvae found in slow-flowing (<0.5 m/s) seston-poor (<10 mg/L) water will tend to have weak fans with a complex structure and larvae found in water with moderate water velocities and moderate seston levels will tend to have a standard fan structure. The model was tested against black flies from other parts of the world, particularly Polynesia, and provides a useful framework for predicting the distribution of black fly species within a catchment. Exceptions to the model were found among phoretic species. The model should predict changes in black fly species in areas where anthropogenic changes to watersheds are occurring.