Death comes suddenly to the unprepared: Singing crickets, call fragmentation, and parasitoid flies

Abstract

Male field crickets are subject to a delicate dilemma because their songs simultaneously attract mates and acoustic predators. It has been suggested that in response, crickets have modified various temporal song parameters to become less attractive to acoustic predators. We investigated whether crickets with chirping (versus trilling) song structures are less likely to attract acoustically orienting parasitoid flies. Experimentally, we evaluated the phonotactic quest of the parasitoid fly Ormia ochracea in response to broadcast cricket calls, presented both simultaneously (choice paradigm) and sequentially (no-choice paradigm). Flight trajectories were recorded in darkness using three-dimensional active infrared video tracking. The flies showed remarkable phonotactic accuracy by landing directly on the loudspeaker. The introduction of acoustic fragmentation that resembles calls of many chirping crickets altered the flies' phonotactic accuracy only slightly. Our results document differential attraction between trilling and chirping cricket songs and quantitatively demonstrate that chirping songs, if presented alone, do not impair the efficiency (temporal investment and landing accuracy) of the flies' phonotactic quest. This study shows that song fragmentation is no safeguard against acoustic parasitism. We conclude that, in general, a cricket may reduce predation only if its neighbors are acoustically more conspicuous, chiefly by amplitude.