Aerobic Bacterial Flora of the Larval Gut of the Black Fly Prosimulium Mixtum (Diptera: Simuliidae) from Newfoundland, Canada

Abstract

A comparative study was made of the aerobic bacterial flora of the larval gut of the black fly Prosimulium mixtum and of the surrounding Broadcove River water. The distribution of Gram-positive and Gram-negative bacteria was also studied by histochemical means. A total of 13 bacterial and fungal species were identified from the gut, and a total of 11 bacterial species were isolated from Broadcove River. The levels of viable cells were low in both the gut (0.55%) and in the river (0.39% to 0.50%). The bacteria Serratia marcescens, Micrococcus luteus, M. roseus, Alcaligenes faecalis and Streptococcus faecalis zymogenes were isolated only from the river. The bacteria Bacillus sp., B. amyloliquifaciens, B. circulans, B. macerans and Corynebacterium bovis were isolated only from the gut. Representatives of C. bovis and Flavobacterium sp. comprised relatively high proportions of the gut flora and were presumably either selectively concentrated during feeding or favored in their growth by the gut environment. The total bacterial counts indicated approximately a 1,000,000-foid increase in cell level in the gut over that in the river water. The histochemical studies indicated the presence of a high concentration of bacteria just posterior to the esophageal valve, a fairly uniform distribution of bacteria in the midgut and a concentration of bacteria along the peritrophic membrane in the hindgut.