A radiotracer method for determining ingestion of Bacillus sphaericus by mosquito larvae

Bacillus sphaericus was labeled with carbon-14 by culturing in a medium containing U-¹⁴C-l-amino acid mixture or d-U-¹⁴C]glucose, the former giving consistently higher labeling. Less than 5% of the label was lost during the 2-hr experimental period. Groups of mosquito larvae were exposed to labeled bacteria for variable times, washed to remove external radioactivity, and then were either analyzed by combustion and liquid scintillation counting for internal ¹⁴C or held in fresh water for mortality counts. Culex quinquefasciatus larvae rapidly ingested bacteria during the first 30 min followed by a reduced rate of accumulation. the rate and quantity of bacteria ingested was greater with later instars. The method is applicable for the study of environmental and physiological factors influencing the ingestion and susceptibility of different species of mosquito larvae to bacterial pathogens.