Ingestion and assimilation efficiency of Aeshna brevistyla and Hemicordulia australiae larvae (Odonata)

In a laboratory study of the ingestion and assimilation efficiency of larvae of Aeshna brevistyla Rambur and Hemicordulia australiae Rambur, ingestion was determined using Cerenkov radiation techniques and assimilation efficiency by a double‐labelled isotope technique. Of each prey item (Daphnia carinata) , 30% was not ingested but lost as body fluids and as material within the alimentary canal of the prey. Assimilation efficiency was greater than 70% for both dragonfly species, which appears to be typical for most other invertebrate predators. The efficiency with which 12th‐15th‐instar Aeshna assimilated 14 C did not increase with feeding rate, but Hemicordulia increased its efficiency through instars 12–14. When dragonfly larvae were pre‐fed before experimentation, assimilation efficiency decreased in both species.