Maximizing collection and minimizing risk: does vacuum suction sampling increase the likelihood for misinterpretation of food web connections?

Molecular tools that characterize the structure of complex food webs and identify trophic connectedness in the field have become widely adopted in recent years. However, characterizing the intensity of predator-prey interactions can be prone to error. Maximizing collection success of small, fast-moving predators with vacuum suction samplers has the potential to increase the likelihood of prey DNA detection either through surface-level contamination with damaged prey or direct consumption within the sampling device. In this study, we used PCR to test the hypothesis that vacuum suction sampling will not cause an erroneous increase in the detection of 'predation', thereby incorrectly assigning trophic linkages when evaluating food web structure. We utilized general (1) Aphidoidea and (2) Collembola primers to measure the predation rates of Glenognatha foxi (Araneae: Tetragnathidae) on these prey collected by hand versus those sampled with a vacuum suction device. With both primer pairs, there was no significant increase in predators screening positive for prey DNA when sampled by vacuum suction versus those predators collected, in parallel, by hand. These results clearly validate the application of vacuum suction sampling during molecular gut-content analysis of predator-prey feeding linkages in the field. Furthermore, we found no evidence that predation was occurring inside the suction sampler because specimens collected were never observed to be feeding nor did they screen positive at greater frequencies than hand-collected individuals. Therefore, it can be concluded that the use of vacuum suction sampling devices (in this case a Modified CDC Backpack Aspirator Model 1412) is suitable for molecular gut-content analysis.