The efficiency of kerosene flotation for extraction of chironomid head capsules from lake sediments samples

Kerosene, a grade mineral oil, is commonly used to extract beetles from sediment. Here, the use of kerosene to extract chironomid head capsules was tested on 10 samples from sediment of different lakes, with different organic matter content as measured by loss on ignition, and estimated ages. Our results revealed that this flotation tool is very effective in extracting either full or half chironomid head capsules. The mean extraction efficiency was 89.3 ± 8.0% with an estimated relative abundance error ranging from −1% to 1% for 46 of the 57 identified taxa. Larger chironomids (400–500 µm width), which are often full of sediment particles, have the highest relative abundance error, with a maximum of 4.3% for Corynocera oliveri-type. A canonical correspondence analysis showed that, despite this small bias, samples retrieved with the kerosene flotation do not differ from the whole sample assemblages. These results give us confidence in the use of this flotation technique for chironomid sample preparation.