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Breaking the code: interception and exploitation of intraspecific vibrational communication between insects by generalist predators

Final Activity Report Summary - BREAKING THE CODE (Breaking the code: interception and exploitation of intraspecific vibrational communication between insects by generalist predators)

Aphrodes leafhoppers are small insects, common on a range of herbaceous plants. Males and females communicate through vibrational signals which are transmitted through the stems and leaves of plants from one sex to the other, enabling the leafhoppers to recognise and find one another in thick vegetation. Unlike visual signals, pheromones and air-borne acoustic signals, it was thought that these vibrational signals were a private channel for sexual communication, being unlikely to be detected by predators.

Nevertheless, we thought that potentially spiders, many of which catch prey by detecting vibrations on webs or foliage, could be intercepting these signals and use them to locate and catch the leafhoppers. The first task was to investigate which spiders’ species were eating leafhoppers in the field. To do this, we developed a method of detecting the deoxyribonucleic acid (DNA) of the leafhoppers in the spiders’ guts. This DNA would only be present if an aphrodes was consumed within the previous few days. We did this on a range of spider species, expecting that wolf spiders in particular would be leafhopper predators because they were active hunters that did not build webs. As is turned out this was not the case. The most numerous predator of aphrodes at the field site was the cobweb spider enoplognatha ovata. Up to 25 % of these spiders had aphrodes DNA in their guts, despite the fact that a myriad of other, more abundant preys, were available to them.

We then conducted feeding trials in the lab with both wolf spiders, i.e. pardosa amentata, and cobweb spiders. The pardosa wolf spiders did not eat live aphrodes even when no other prey was available, confirming our field results. However, enoplognatha not only reduced aphrodes numbers but also showed a preference for males. As males produced a stronger and more complex vibrational signal than the females, this preference was further evidence that it was the signals that the spiders employed to find their prey. We then utilised a laser vibrometer to record and play back the male leafhopper vibrational signal to spiders through plant leaves. Interestingly, the cobweb spiders spent more time on the plants when male vibrational signals were being played. This was not the case when we played female signals or the sound of a walking insect, suggesting once again that the strong signal of the males affected the behaviour of cobweb spiders. Wolf spiders showed no significant response to any of the signals.

We concluded from the abovementioned evidence that the cobweb spider enoplognatha ovata did actually use the vibrational signals of male aphrodes to home in on its prey. This was a phenomenon rarely detected in any predator and never observed in spiders before this research project.