How does dung burial by coprophagous beetles modify the emergence of infectious strongyle nematode larvae? An experimental test across different soil depths

During their free-living stage, gastrointestinal nematode (GIN) eggs and larvae may encounter environmental and biomechanical perturbations, such as dung beetle (Coleoptera: Scarabaeidae, including Aphodiinae, Scarabaeinae and Geotrupidae) activity, that could alter their survival. However, dung beetles’ influence in promoting or suppressing nematodes' survival is poorly understood. Past work suggests that the burial of dung underground by dung beetles may either suppress nematode infections, limiting larval emergence above ground, or enhance nematode infections by creating favourable microclimates for eggs and larval development. We examined the effect of simulated burial of wildebeest dung at four soil depths on the density of infectious third-stage larvae (L3) on herbage over a 42-day window in the Serengeti ecosystem. GIN larval density was highest from dung buried at 5 and 10 cm depths below the soil surface, and lowest at 0 cm (on the surface) and 15 cm depths. This suggests that dung beetles may facilitate L3 survival and emergence by creating favourable conditions at shallow depths (5-10 cm), protecting them from disturbances (e.g., desiccation) on the surface. Deeper burial depth (15 cm) by dung beetles, however, appears to suppress the emergence of L3 by creating a physical barrier to upward migration. Across burial depths, L3 density peaked on Day 14 and declined on Days 28 and 42, with no evidence that deeper burial led to a prolonged emergence period. These results reveal dung beetles' complex role in parasite ecology, not merely as suppressors of these free-living stages but also as facilitators of their survival through burial activities that vary with depth. Incorporating this knowledge into pasture and insect management could support the use of dung beetles as potential biological control agents against gastrointestinal nematodes.