Eavesdropping, or signal exploitation, is a common and natural phenomenon in which organisms detect and respond to information that was not intended for them. Moreover, the distinction between signals and noise, and between intended and unintended receivers, is less debatable with sexual signals, such as pheromones, in which mates are obvious targets and non-mates are obvious eavesdroppers. Pheromonal eavesdropping between natural enemies and their prey or hosts is especially common. Eavesdropping, however, between organisms that do not prey on or readily compete with each other is far less common. In the past few years, multiple species of insect herbivores that seemly coexist with each other were found attracted to vittatalactone, the main chemical component of Acalymma vittatum - striped cucumber beetle - pheromone. Although it remains unclear what other organisms might be responding to vittatalactone, a more important question to investigate is why other organisms, especially other herbivores, are responding, given that decades of past research have revealed risky tradeoffs associated with signal exploitation such as increased consciousness and competition. In this study, we investigated the attraction to vittatalactone in two organisms, a known eavesdropping herbivore, Anasa tristis, and a potential eavesdropper, a common parasitoid natural enemy of striped cucumber beetle, Celatoria setosa (Diptera: Tachinidae). We then investigated the costs and benefits of pheromonal eavesdropping in both species using a combination of lab and field experiments. Here we report on those findings and discuss pheromonal eavesdropping in a broader context for emitters and receivers.
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