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Urbanization can affect arthropod abundance in different ways. While species with narrow habitat range and low dispersal ability often respond negatively to urban environments, many habitat generalist species with good dispersal ability reach high densities in city centers. This filtering effect of urban habitats can strongly influence predator-prey-mutualist interactions and may therefore affect the abundance of predatory and phytophagous species both directly and indirectly. Here, we assessed the effect of urbanization on aphids, predatory arthropods, and ants on field maple (Acer campestre) trees in and around the city of Budapest, Hungary. We used the percentage of impervious surfaces within a 500 m radius of each site as an index of the degree of urbanization. We found that the abundance of aphids increased with increasing level of urbanization. However, abundance of predatory arthropods and occurrence of poorly dispersing species within the predator community were negatively related to urbanization, and we identified these two independent factors as significant predictors of aphid abundances. The abundance of ants decreased with urbanization, and contrary to our expectations, did not affect the abundance pattern of aphids. Our results suggest that urbanization, by altering the abundance and composition of predator communities, can disrupt biological control of aphid populations, and thus may contribute to the aphid outbreaks on urban trees.

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A detailed description of the spectrographic and oscillographic features of the male calling song of Saga rammei is presented for the first time. The study is based on Macedonian specimens. The song of S. rammei is a mainly amplitude-modulated signal having wide-band frequency spectrum containing well detectable frequency components between 15 kHz and 80 kHz (intensity maximum between 20–30 kHz). The male song is a sequence of echemes, which are composed of evenly and quickly repeated diplo-hemisyllabic syllables. Echemes begin with a gradually crescending initial part that leads to the main part of the echeme, where the peak amplitude of the syllables is nearly constant. This structure is similar to those described in other European Saga species (S. hellenica, S. campbelli, S. natoliae). However, the results suggest that amongst the European Saga species S. rammei produces the shortest echemes composed of the lowest number of syllables repeated with the highest syllable repetition rate and that the species sings with the shortest echeme repetition period. Those quantitative features make the song of S. rammei distinct and easily recognisable, and therefore could be used by females or males for species recognition.