| Summary: | This study Is concerned with the behavioural and ecological aspects of the acoustic interaction that occurs when two bush cricket species, Platycleis albopunctata and Metrioptera roeselii. sing together. The effects of the interaction are predominantly one-way and result in inhibition of singing activity by albopunctata, or a change in its song pattern. 'Ibis behaviour was initially described by Broughton in I965 who also described song changes in other species resulting from interactions with singing allospecifics. The present study continues this research into song modification in insects. The extent of natural variation is examined in detail in the song of albopunctata. The acoustic behaviour of this species when singing with conspecifics is also examined in detail. The songs and singing behaviour of some other bush cricket species are analysed and tested for susceptibility to modification. These latter studies, though less detailed than the study on the albopunctata/roeselii interaction, have contributed to the formation of hypotheses as to the causation of song modification. The results indicate that insects with songs of similar frequency content are liable to interact acoustically. Species which show slight readjustments in song output when singing with conspecifics are also liable to song modification especially when the song of the influencing Insect is more continuous in nature than the song of the Influenced insect. The results of the detailed analysis of the albopunctata/roeselii interaction reveal a complex interplay between endogenous rhythms of motivation displayed in the singing activity of albopunctata, and parallel inhibitory and excitatory factors from the song of the roeselii. Much of the fieldwork has been undertaken in France v/here, in many localities, albopunctata and roeselii are sympatric. Song modification in the wild is usually prevented by a negative phonotactic response by albopunctata to the song of roeselii» This response may be derived from preexisting behavioural patterns that result in 'territorial' spacing between males in grassland populations. In habitats where populations overlap, interspecific spacing develops with the onset of singing activity by the adults. In this way albopunctata is excluded from certain localities by high-density roeselii populations due to the acoustic competition between these two species.
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