Ginger traps and miniature microphones are key to conserving the UK’s largest terrestrial beetle – the stag beetle, say researchers in London and York.
An adult male stag beetle Credit Deborah Harvey
The researchers developed a series of new methods to monitor stag beetle numbers, including heavy duty plastic traps containing ginger and tiny microphones to detect sounds made by their larvae in underground nests.
“Our new methods offer genuine promise for monitoring the population of this elusive and rare insect, one that we think is declining across much of its European range,” said Dr Deborah Harvey from Royal Holloway. “We need to know where the stag beetle lives – and in what numbers – to be able to conserve it effectively.”
Harvey and her colleagues tested the attractiveness of many fruit and vegetables before discovering ginger was irresistible to the adult beetle. Ginger contains large amounts of alpha copaene, a chemical known to attract other insects that live in dead and decaying wood.
Other methods of trapping the insects – such as light traps or traps baited with food – failed to work as adult stag beetles are not reliably attracted to light, nor do they eat during the adult phase of their lives.
Dr Harvey also needed to monitor levels of larvae living underground, without disturbing their habitat and turned to Dr David Chesmore from the department of electronics at the University of York. They used tiny microphones to record stridulation – the sounds the larvae make – together with diffuse samplers to detect the chemical longifolene they emit.
“Sampling subterranean insects without destroying the larval habitat is notoriously difficult,” Harvey said. “These diffuse samplers are widely used to monitor environmental pollution but this is the first time they have been used for insect detection.”
“Until now, it has been very difficult to monitor the beetle’s distribution without damaging the habitat,” Chesmore said. “We have discovered not only that the larvae of the stage beetle can be detected using acoustics but the sounds are different from other species likely to feed in the same habitat.”
In addition to recording stag beetle larvae, the team also made the first ever sound recording of the lesser stag beetle and the rose chafer larvae, which sounds like a squeaking shoe. They hope their methods could be used to conserve other rare species.