A comparison of methods for extracting Coleoptera and Hemiptera from wetland net sweep samples

Abstract Time and effort required to extract macroinvertebrates out of aquatic net sweep samples can be a major limiting factor in the ecological study and monitoring of wetlands. Several methods for facilitating specimen extraction have been published, but systematic comparisons are lacking. We opportunistically compared six methods for extracting macroinvertebrates from wetland net sweep samples that we collected in Alberta, Canada. We applied elutriation, flotation using four different media, and a new behavioural extraction method using a submerged inverted funnel. We measured the length of time each method took to extract all perceived macroinvertebrates and the proportion of Coleoptera and Hemiptera that each method successfully extracted. Elutriation and flotation using a 600 g/L sugar–water solution extracted the greatest proportions (> 95%). Elutriation was faster than flotation with our samples. The faster behavioural method extracted only approximately 50–70% of specimens; however, it produced clean samples for subsequent sorting. Overall, we recommend elutriation for reliable extraction of Coleoptera, Hemiptera, and other macroinvertebrates from wetland net sweep samples. Refinement of our behavioural extraction method may lead to an effective field-based alternative to time-consuming laboratory-based extraction methods.