Feeding activity of soil oligochaetes under different soil moisture regimes assessed by the bait-lamina test.

The bait-lamina test is an easy and efficient method to quantify the feeding activity of soil invertebrates, commonly performed under field conditions to measure the impact of chemicals on soils. However, under natural conditions, feeding activity is also influenced by environmental factors such as soil moisture content. The extent of this influence on the results of the bait-lamina test is still poorly described and this can complicate their interpretation. In this study, we optimized the bait-lamina test under laboratory conditions, to assess the influence of soil moisture content on feeding activity of the earthworm Eisenia andrei and the enchytraeid Enchytraeus albidus, using LUFA 2.2 soil as a substrate. Feeding activity increased linearly with increasing soil moisture until a peak was reached, at a moisture content of 52 % of the maximum water holding capacity (WHC) for earthworms, and 68 % WHC for enchytraeids. Above the optimal moisture content, feeding activity was reduced and was less dependent on soil moisture. The increase in feeding activity up to the optimal moisture content was described by different slopes for the two species. Earthworms consumed the bait faster (on a per unit weight basis) than enchytraeids. Among the two species, the relationship established for E. albidus was the more similar to the response obtained in field conditions. Within the range of soil moistures considered by the model, our results demonstrate that feeding activity is positively correlated with soil moisture for two important soil invertebrates, but this increase, as well as the optimal soil moisture content, and the speed of bait consumption are species dependent. The model produced represents a first step for normalizing results from bait lamina tests in the field laying the foundation for future studies to validate its applicability across different soil types and field conditions. HighlightsThe optimal soil moisture leading to peak feeding activity was of 52 % and 68 % WHC for E. andrei and E. albidus respectively. Earthworms consumed the baits more than three times faster than enchytraeids. The influence of soil moisture on feeding activity up to the peak can be described by a linear model the slope of which depends on the species tested. The model obtained for E. albidus best represented the field situation.