Feeding rates of fourth instar larvae of Aedes vexans were compared by counting substrate filled gut segments after exposure to food or inert particles. Food particles (wheat flour, fishmeal or yeast) were ingested approximately 3 times faster than inert particles (kaolin, pumice or synthetic cellulose). Aqueous fishmeal extract accelerated ingestion of inert particles to the level of ingestion of food particles, demonstrating gustatory stimulation of larvae. Absolute amounts of ingested materials were calculated on the basis of dry weights of guts completely filled with test substrates. At 21 degrees C, 46-74 micrograms of food particles, and 15-33 micrograms of inert particles were ingested per larva during 10 min of exposure. In the subsequent time span, ingestion rates of food particles decreased continuously with satiation of larvae.