The normal feeding behavior of Simulium vittatum larvae was disrupted following exposure to high concentrations of suspended particles under simulated stream conditions. Virtually all particulates tested caused inhibition of feeding at a concentration of 50 mg/liter, indicating that inhibition is a nonspecific response. The percentage of larvae with inhibited feeding increased with increasing particle concentration. Our results indicate that inhibition was a consequence of rapid gut filling.

The pathogenicity of Bacillus thuringiensis var. israelensis against S. vittatum was diminished or enhanced depending on whether feeding inhibition was induced before or after bacterial exposure. These results were attributed to reduced rates of bacterial ingestion and voidance, respectively. Such effects may have important implications in laboratory bioassays and field control.