Background noise disrupts host-parasitoid interactions

Abstract

The soundscape serves as a backdrop for acoustic signals dispatched within and among species, spanning mate attraction to parasite host detection. Elevated background sound levels from human-made and natural sources may interfere with the reception of acoustic signals and alter species interactions and whole ecological communities. We investigated whether background noise influences the ability of the obligate parasitoid Ormia ochracea to locate its host, the variable field cricket (Gryllus lineaticeps). As O. ochracea use auditory cues to locate their hosts, we hypothesized that higher background noise levels would mask or distract flies from cricket calls and result in a decreased ability to detect and navigate to hosts. We used a field manipulation where fly traps baited with playback of male cricket advertisement calls were exposed to a gradient of experimental traffic and ocean surf noise. We found that increases in noise amplitude caused a significant decline in O. ochracea caught, suggesting that background noise can influence parasitoid-host interactions and potentially benefit hosts. As human-caused sensory pollution increases globally, soundscapes may influence the evolution of tightly co-evolved host-parasitoid relationships. Future work should investigate whether female cricket phonotaxis towards males is similarly affected by noise levels.

Keywords: Gryllus lineaticeps; Ormia ochracea; experimental playback; host–parasitoid interactions; noise pollution; soundscape.

Figure 1.

Power spectra of traffic (red) and ocean surf (blue) illustrate strong masking potential of cricket advertisement calls (teal). Traffic and ocean surf noise files were standardized to the same peak amplitude prior to comparison.

Figure 2.

Schematic of general experimental design. Green cubes denote the speaker (either 2 TIC GS5 or one Block Rocker speaker). Each black oval represents a speaker broadcasting a unique cricket advertisement call and blue squares represent wood panels treated with Tanglefoot.

Figure 3.

Power spectra comparison of a single original traffic file recording (blue) and the same recorded following playback from TIC GS5 speakers (teal) and Block Rocker (red). Vertical dashed lines correspond to signal peaks for cricket calls.

Figure 4.

Increases in traffic noise or ocean surf sound resulted in fewer O. ochracea caught at cricket advertisement call traps. Y-axis reflects the natural logarithm of number of flies caught plus one.