An effect of dung beetle activity on plant yield

The effect of the activity of dung beetles (Scarabaeids) on plant growth was investigated in glasshouse experiments in Canberra in 1965 with Onthophagus australis Guer., which feeds principally on marsupial droppings but is also attracted to the faeces of bovine and other introduced domestic animals [cf. RAE/A 57, 2153], as test insect. Comparisons were made of the yield and uptake of nutrients in plants of Japanese millet (Echinochloa crusgalli var. frumentacea) growing in pots in soil deficient in nitrogen, phosphorus and sulphur that was treated with fresh cow-dung in the presence or absence of adults of O. australis or was given applications of two or three of the plant nutrients in mineral form prior to sowing. Yields of top growth and roots were increased substantially where the dung was intimately mixed with the soil, to a rather less extent in pots with both dung pats and beetles, and only slightly in pots with dung pats alone. The first two treatments also caused appreciable increases in the uptake of nitrogen, phosphorus and sulphur from the soil, comparable to those following applications of the nutrient minerals in the case of nitrogen and phosphorus and higher in that of sulphur. In pots in which the dung pats were removed prior to sowing and in pots without dung in which beetles were present or their action was simulated, yields and the uptake of nutrient elements were similar to those in the untreated controls. Root growth was concentrated near buried dung. Unpublished observations by the senior author showed that O. australis buries an average of 10% of bovine dung in spring and autumn, and it is therefore considered to be of value in the nutrient cycle of grass and in the tableland districts of New South Wales.