Interactions between food quantity and quality (long-chain polyunsaturated fatty acid concentrations) effects on growth and development of Chironomus riparius

Abstract

We quantified somatic growth, development, and emergence of the midge Chironomus riparius on experimental diets (oats, Spirulina, and Tetraphyll®) covering gradients in food quality (differing polyunsaturated fatty acids) and quantity (0.1–5.4 mg C·day–1). Additionally, similar incubations without food additions were made using a food-poor sediment containing peat and the green alga Scenedesmus obliquus. Larval and adult size was affected by both food quantity and quality and increased some three to four times across the food concentration gradients. Adult emergence, however, was affected only by food quantity. A type 3 response model showed that a saturation level was reached for the oats treatment at 2.7 mg C·day–1 (or 3.9 µg ω3 and 120 µg ω6 polyunsaturated fatty acids·day–1), indicating that the quality of oats constrained further stimulation of larval growth. In the peat treatment, larval growth was very low, no adults emerged, and no larvae even made it to the pupa stage. Fatty acid analyses showed that larvae were capable of synthesizing arachidonic acid via γ-linolenic acid by Δ6- and Δ5-desaturase activity using linoleic acid available in food sources. This strongly suggests that C. riparius is not dependent on dietary sources of eicosapentaenoic acid and arachidonic acid and can sustain viable populations even under a low-quality food regimen.