Dung beetles, biological control agents against gastrointestinal nematodes in livestock: In vitro test

The control of gastrointestinal nematodes (GIN) remains a major challenge in grazing cattle, due to the widespread of anthelmintic resistance and limited treatment alternatives. This study aimed to assess whether dung beetles could serve as biological control agents against GIN infective larvae (GIN-L₃). Four dung beetle species (Digitonthophagus gazella, Onthophagus australis, Euoniticellus intermedius, and Copris incertus) were collected from cattle paddocks. For each species, their effect on the vertical distribution of GIN-L₃ in soil was assessed using vertical terrariums containing sterilized soil and marked at 5 cm intervals from 0 to 25 cm. GIN-infected calf stool (635.3 ± 77.62 epg) was placed on top, and five couples of dung beetles were introduced. Three replicates were run for each treatment and control. Soil layers were individually recovered after 10-days, GIN-L₃ were retrieved, quantified, and identified. In the absence of dung beetles, and similar to O. australis, 84.9 ± 3.8 % of GIN-L₃ remained in the feces; while C. incertus and D. gazella concentrated 58 % and 49 % of GIN-L₃ between 10 and 25 cm depth, respectively (P < 0.05). The GIN-L₃ density increased by 14.12 % for each brood mass present at ≥ 15 cm depth. Cooperia punctata L₃ artificial burial assay showed a 28 % decrease in its upward migration capacity (R²=0.92) per centimeter of depth; meaning deep tunnelers reproductive behavior hinders GIN-L₃ from reaching the surface and continuing its life cycle. These findings provide new insights into the role of dung beetles in modulating the vertical distribution of GIN-L₃ in soil, and thus, their potential to reduce pasture infectivity, supporting their inclusion in integrated strategies for GIN control.