Interspecific competition between two field populations of grass-feeding bugs

Abstract. 1. We tested the hypothesis that interspecific competition between two grass-feeding stenodemine bug species ( Notostira elongata Geoffroy and Megaloceraeu recticornis Geoffroy) was capable of causing population-scale mortality in the field.
2. N.elongata nymphs were added to two field enclosures in which the M.recti-cornis population was to hatch. In one of these enclosures the grass Arrhena-therum elatius L., on which only M.recticornis can feed, was also added. Population changes of the bug species were then monitored. An unmanipulated enclosure and an unfenced plot of grassland were used as controls.
3. The results demonstrated that N.elongata lowered the survival of M.recticornis and that this effect was removed by the addition of A.elatius . The results also suggested that N.elongata suffered less from the effects of competition with M.recticornis when the latter had access to the refuge foodplant.
4. Interspecific competition was rare among members of the grass-feeding stenodemine guild in the area studied. Only one out of fifteen possible pairs competed, and this competition occurred only under special circumstances.