VARIATIONS IN THE AMINO-ACID CONTENT IN ZEBU DUNG IN THE SAHEL DURING NESTING BY DUNG-BEETLES (COLEOPTERA, SCARABAEIDAE)

The variations in amino-acid concentration and nature in organic matter derived from zebu dung have been studied in the Niger around Niamey. In the dry season, the dung, deposited by the zebu on fields later used to grow millet and not ploughed in by the farmers, is incorporated into the soil by coprophagous Coleoptera. With this excrement they build nests in which their immature larval instars can develop. Once the dung has been deposited, analysis of the amino-acids in the zebu dung, in the nests and the pupal shells of the three species of dung-beetle (Onitis alexis. Onthophagus gacella and Euoniticellus intermedius), has enabled us to follow the changes supported by these amino-compounds. Subject to evidence that gaseous nitrogen is directly fixed in the digestive tracts of the larvae of these coprophagous insects, the increase in the total amino-acid concentration of the pupal shell compared to the nest is proof that the organic nitrogen of the dung is used by symbiotic micro-organisms of the immature larval instars. In O. alexis the concentration of 6 amino-acids (prolinc. glycine, aluninc, diaminopimelic acid, glucosaminc and galactosaminc) out of the 20 encountered increase by over 100%. The amino-acids thus synthesized arc partly used by the larva, and partly concentrated in the products of its excretion and digestion. © 1990.