The feeding and tunneling activities by insects alters the physical and chemical properties of cattle dung and potentially affect greenhouse gas (GHG) emissions. To determine the magnitude of these effects on semiarid pastures, we quantified GHG emissions (CO2, CH4 and N2O) from beef cattle dung pats with or without insect activity (e.g., dung beetles) and with or without ivermectin. Ivermectin is a commonly used parasiticide to treat cattle and was added to the dung to reduce insect activity. Exclusion of insect activity was achieved by covering the chambers with a nylon mesh to prevent insects from interacting with the dung pats. The mesh did not affect gas exchange between the chamber and atmosphere. The GHG fluxes were measured over one year at weekly intervals in the grazing season and less frequently in the non-grazing season. Dung and soil samples were collected and analyzed for moisture and available C and N contents at weekly intervals for the first three weeks, and less frequently thereafter. The CO2 emitted from dung pats without insect activity was nearly double that of dung pats with insect activity. The CH4 emitted from dung pats without insect activity was more than double that of dung pats with insect activity reduced by adding ivermectin, but with less differences when compared to dung pats without ivermectin. The N2O emitted from dung pats without insect activity was more than double that of dung pats with insect activity. Ivermectin had limited effect on CO2 and no effect on N2O emissions. The CH4 flux appeared to be responsive to both ivermectin and insect activity. More research is required to verify the results observed in this one-year study. The feeding and tunneling activities of insects appears to play an important role mitigating the GHG emitted from dung pats on semiarid pastures.
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