Phagostimulant Effects of Simple Nutrients on Larval Culex pipiens (Diptera: Culicidae)

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Abstract
We examined the influence of various crude and simple nutrient solutes on the rate of ingestion by larvae of the mosquito Culex pipiens L. of particulate solids filtered from ambient water. Various crude organic solutes and mosquito synthetic dietary medium, a mixture of about 40 pure nutrients, were strongly phagostimulatory. Of well-defined chemicals tested, only nucleic acids and yeast adenylic acid were strong phagostimulants. Among sugars tested, mannose, maltose, and sucrose were stimulants, but glucose, sorbose, fructose, galactose, and ribose had little or no effect or were slightly inhibitory. Several protein hydrolysates were phagostimulant. A mixture of the 20 amino acids used in synthetic diet was moderately stimulant, but when tested individually only arginine, aspartic acid, tryptophan, and tyrosine had significant stimulatory effects. Except for moderate stimulation by phosphate ion, most salts tested, variously comprising sodium, potassium, chloride, nitrate, and sulfate ions, were without effect at molarities of 0.05, except that calcium seemed phagoinhibitory. The effects of phosphates may have been partly a function of pH, since phosphate buffers were inhibitory below pH 6 and were stimulatory only at pH greater than 8. Omission of various classes of nutrient from otherwise complete diet had no effect except that omission of nucleotides in one experiment reduced ingestion rate appreciably. This suggests that strong stimulation by complex organic solute mixtures can be an additive effect of several individually moderate and weak phagostimulants. The ecological significance of dissolved nutrients acting as phagostimulants for an omnivorous filter feeder is discussed.