Posted on 10 January 2011
Electronic engineers from the University of York teamed up with ecologists from Royal Holloway, University of London to develop a series of new methods to monitor stag beetle numbers – including ginger lures to trap adult beetles and tiny microphones to detect sounds made by the larvae in their underground nests. Conservation efforts have been hampered until now because ecologists lacked a reliable way of monitoring stag beetle numbers.
The new research, published in the Royal Entomological Society's journal Insect Conservation and Diversity, found that a combination of ginger-baited aerial traps to catch adult stag beetles, plus tiny microphones to record the underground larvae's sounds and samplers to detect the chemicals they emit, give an accurate picture of the species' abundance.
Dr David Chesmore from the Department of Electronics at the University of York said: “Until now, it has been very difficult to monitor the beetle's distribution without damaging the habitat. York's contribution to the project has been on acoustic detection. We have discovered not only that the larvae of the stag beetle can be detected using acoustics but the sounds are different from other species likely to feed in the same habitat. This means that we will be able to discriminate between the different species and we are developing electronic systems to achieve this."
Ecologists from Royal Holloway, University of London discovered ginger was irresistible to adult stag beetles only after testing the attractiveness of many other fruit and vegetables – including banana, strawberry, tomato and cherry – as well as wine and beer. Ginger works because it contains large amounts of alpha copaene, a chemical known to attract other insects that live in dead and decaying wood.
By using ginger, and designing the trap using heavy duty plastic, the team was able to produce a very cost-effective trap, which is vital because most insect monitoring in the UK is done by a small army of dedicated but unfunded amateur recorders.
Using other methods of trapping insects, such as light traps or traps baited with food, do not work with adult stag beetles because they are not reliably attracted to light and the species does not eat during the adult phase of its life cycle.
We have discovered not only that the larvae of the stag beetle can be detected using acoustics but the sounds are different from other species likely to feed in the same habitat
Dr David Chesmore
As well as finding a method of monitoring adult numbers, the team also needed a way to detect larvae, which live underground. Hand searching is likely to destroy their habitats, so instead they used tiny microphones to pick up the sounds – known as stridulation – the larvae make, together with so-called diffusive samplers to detect a chemical (longifolene) they emit.
Dr Deborah Harvey, Royal Holloway, University of London, said: “Sampling subterranean insects without destroying the larval habitat is notoriously difficult. These diffusive samplers are widely used to monitor environmental pollution, but this is the first time they have been used for insect detection. Because longifolene can be produced by plants, we used it together with sound recording to come up with a more accurate method of finding stag beetle larvae.”
The team found that stridulation patterns produced by stag beetle larvae are very different from other species likely to live nearby, such as the rose chafer (Cetonia aurata) and the lesser stag beetle (Dorcus parallelipipedus). “Stridulation is likely to be a form of communication between larvae; it increases if larvae are handled or placed in solitary confinement,” Dr Harvey said.
These are the first ever sound recordings of lesser stag beetle and rose chafer larvae. The latter sound like squeaky shoes.
The new methods could help conserve other rare species. Dr Chesmore said: “Acoustic detection of insects as a sampling method is very underused, but we believe it could have great potential in detecting larvae in the field.”
The study was funded by the British Ecological Society, the Forestry Commission, the People's Trust for Endangered Species and the Suffolk Naturalists' Society.