A priori
knowledge of fatty acid modifications in consumers is essential for studies using fatty acids as biomarkers. We investigated fatty acid metabolism and possible modification pathways in benthic invertebrate
Chironomus riparius
larvae (Diptera). We conducted diet manipulation experiments using natural food sources (two chlorophyte algae, a diatom and a non-toxic cyanobacterium). We also did a diet-switch experiment on two different resources, fish food flakes TetraMin
®
and cyanobacterium
Spirulina
, to study fatty acid turnover in
Chironomus
. Results of the diet manipulation experiments indicate that
Chironomus
larvae have a strong tendency to biosynthesize 20:5n-3 and 20:4n-6 from precursor fatty acids, and that the dietary availability of polyunsaturated fatty acids (PUFA) does not control larval growth. Fatty acid modifications explain why low dietary availability of PUFA did not significantly limit growth. This has ecologically relevant implications on the role of benthic chironomids in conveying energy to upper trophic level consumers. A diet-switch experiment showed that the turnover rate of fatty acids in
Chironomus
is relatively fast––a few days. The compositional differences of algal diets were large enough to separate
Chironomus
larvae into distinct groups even if significant modification of PUFA was observed. In summary, fatty acids are excellent dietary biomarkers for
Chironomus
, if modifications of PUFA are considered, and will provide high-resolution data on resource use.
This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.