OVIPOSITION OF THE DUNG BEETLE APHODIUS ATER IN RELATION TO THE ABUNDANCE OF YELLOW DUNGFLY LARVAE (SCATOPHAGA-STERCORARIA)

1. The dung beetle Aphodius ater and the yellow dungfly Scatophaga ste rcoraria are temporally co-occurring species in sheep dung, which they use for reproduction and nutrition (A. ater) or for reproduction only (S. stercoraria) during the spring In northern Germany. Scatophaga st ercoraria uses fresh sheep dung pellets a few hours old for ovipositio n, whereas A. ater lays eggs into 2-10-day-old pellets. In the present study, the egg laying behaviour of A. ater in sheep dung in relation to the presence of larvae of S. stercoraria was investigated experimen tally. 2. Choice experiments, based on examining the egg laying behavi our of beetles in 2- and di-day-old pellets with and without high and low densities of fly larvae, showed the following. In 2-day-old pellet s, the beetles did not distinguish between pellets without fly larvae or with fly larvae at low larval density but avoided laying eggs into pellets with a high larval density, In 4-day-old pellets, the beetles always preferred to lay their eggs into pellets without fly larvae, re gardless of larval density. 3. The influence of different densities of larvae of S. stercoraria on dung depletion was examined by measuring the dry weight, organic matter content and organic nitrogen content of the remaining dung after larval development. The presence of the larv ae led to a reduction in all three parameters. 4. The beetles' behavio ur of laying eggs into older pellets, and their awareness of the prese nce of high densities of fly larvae, enables them to avoid egg laying into pellets that will have been depleted by fly larvae before the bee tle larvae have finished their development.