ORIGINAL PAPER Chemical ecology and insect conservation: optimising pheromone-based monitoring of the threatened saproxylic click beetle Elater ferrugineus Glenn P. Svensson • Christoph Liedtke • Erik Hedenstro ¨m • Palle Breistein • Joakim Ba ˚ng • Mattias C. Larsson Received: 27 April 2011 / Accepted: 19 September 2011 / Published online: 27 September 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Elater ferrugineus is a saproxylic click beetle inhabiting old deciduous trees in Europe. It is threatened throughout its area of distribution due to habitat loss. No efficient monitoring method has been available for this species, but observed attraction of females to (R)-(?)-c- decalactone, which is a male-produced sex pheromone of its prey, the scarab beetle Osmoderma eremita, has led to the development of an odour lure for monitoring. In addition, four esters have recently been identified from the pheromone-producing gland in female E. ferrugineus, and a blend of these esters is highly attractive to conspecific males in the field, revealing an alternative odour-based method for monitoring this species. However, no rigorous analysis has been performed to check whether all four esters show biological activity in male E. ferrugineus, and whether its own sex pheromone is a more potent lure than the prey kairomone for monitoring of E. ferrugineus. In this study, we reinvestigated the E. ferrugineus sex pheromone, using electrophysiological and behavioural analyses, and found that only one of the esters, 7-methyloctyl (Z)-4-decenoate, is active. In addition, trapping experi- ments revealed that 7-methyloctyl (Z)-4-decenoate is a much more efficient attractant for male E. ferrugineus than the prey pheromone is for conspecific females, or any sex of O. eremita. With a very efficient odour lure at hand, novel information about current distribution, local popu- lation sizes, and dispersal ranges in E. ferrugineus can now be obtained, which can aid in conservation efforts to pro- tect this threatened insect and its habitat. Keywords Elateridae Á Scarabaeidae Á Sex pheromone Á Kairomone Á Field trapping Á Conservation Introduction Effective conservation depends on the ability to reliably measure and monitor changes in species abundance in relation to habitat change. Pheromone-based monitoring has great potential to become an important part of many pro- grams for assessing the conservation status of threatened insects, because sex pheromones are highly species-specific and often efficient in detecting target species at very low densities (Larsson et al. 2009). For many insects, phero- mone trapping thus provides a robust and standardised way of gathering valuable information about population sizes and dispersal ranges. However, the applications of chemical ecology tools have so far been almost exclusively directed towards monitoring and control of pest insects (reviewed by Witzgall et al. 2010), with very little emphasis on the use of semiochemicals in insect conservation and biodiversity studies (but see Gandhi et al. 2009). Consequently, phero- mone identifications for threatened insect species carried Electronic supplementary material The online version of this article (doi:10.1007/s10841-011-9440-5) contains supplementary material, which is available to authorized users. G. P. Svensson (&) Á C. Liedtke Department of Biology, Lund University, Ecology Building, 223 62 Lund, Sweden e-mail: glenn.svensson@biol.lu.se E. Hedenstro ¨m Á P. Breistein Á J. Ba ˚ng Department of Natural Sciences, Engineering and Mathematics, Mid Sweden University, 851 70 Sundsvall, Sweden M. C. Larsson Department of Plant Protection Biology, Swedish University of Agricultural Sciences, P.O. Box 102, 230 53 Alnarp, Sweden 123 J Insect Conserv (2012) 16:549–555 DOI 10.1007/s10841-011-9440-5