The influence of feeding habits on whole‐body metal concentrations in aquatic insects

SUMMARY. Concentrations of seven metals in forty taxa of aquatic insects were determined in order to examine the influence of the insects’ feeding habits on their whole‐body metal content. Species were grouped into five feeding categories which reflected both the type of material the organisms ingested and their contact with sediments during feeding. Species such as the burrowing mayflies (Ephemeridae) and some of the Chironomidae, which indiscriminately ingest sediment along with detritus, had the highest concentrations of most metals. Filter feeders (e.g. Hydropsychidae) had the next highest concentrations, followed by species which to some degree selectively ingest detritus and periphyton (e.g. many Ephemeroptera, Plecoptera and Trichoptera). Carnivores and surface feeding species, such as the Gerridae and Gyrinidae, had the lowest metal concentrations. Analysis of metal concentrations of both gut contents and bodies of individuals from each of these feeding types explain these differences. Gut material was enriched in most metals (Co, Cr, Fe, Sb, Sc) relative to their concentrations in the organism's body and it often constituted a major proportion of an organism's whole‐body burden of a metal. Both the concentrations of metals in the gut material and the proportion of the whole‐body burden of a metal that was associated with gut contents varied with the feeding habit of a species. This was because of differences in the amount of inorganic material ingested by the species in each feeding category, higher concentrations occurring in organisms which ingested relatively greater amounts of sediment. Organism concentrations of K and Na were less affected by feeding habits since the majority of the whole‐body burden of these metals was associated with an organism's tissue and surface rather than with gut material.