Ingestion of colloid solutions by filter‐feeding mosquito larvae: Relationship to viscosity

Abstract

During ingestion tests of 1 to 3 hours duration with larval Culex pipiens, displacement of midgut contents was virtually nil for larvae filterfeeding in particle‐free water, whereas in various dilute colloid solutions displacement was rapid and comparable in rate to displacement in water containing particulate solids. For larvae in 0.01 to 0.1 % methylcellulose solutions or in 0.01 to 0.6% polyhall (polyacrylamide) solutions, having viscosities of approximately 1 to 1.5 or 1 to 3 centipoises, respectively, displacements increased with increasing concentrations from just detectable to maximal and remained maximally high for higher concentrations with viscosities up to 15 and 5 cp respectively. Progressively greater displacements were likewise observed with sucrose solutions of 4 to 20% and having viscosities of 1 to 1.5 cp, but at higher concentrations ingestion was poor because of severe osmotic damage to larvae. In 0.015% agar, which is about 10% more viscous than water, ingestion was virtually nil; but with a doubling of concentration to 0.03%, and with viscosity about 20% greater than for water, displacement was maximal. The correlation between increasing viscosity and increasing ingestion for methylcellulose, polyhall and sucrose implicates viscosity as a factor that may alter the mechanical properties of liquids so as to allow them to be ingested in bulk as readily as particulate solids. With agar, the viscosity difference between non‐ingested and maximally‐ingested concentrations was so small as to suggest that some other factor is involved in bringing about ingestibility, perhaps some property related to the molecular structure that at elevated concentrations of agar brings about the formation of gels.