Intended and unintended receivers of the male pheromones of the burying beetles Nicrophorus humator and Nicrophorus vespilloides

Male Nicrophorus beetles (Coleoptera: Silphidae) attract females through volatiles that are emitted at species-specific times of day. Not only beetles of the opposite sex but also conspecific males are attracted. Another observation is the co-attraction of congeners, a phenomenon that was shown in particular for Nicrophorus vespilloides Herbst, the smallest Nicrophorus species in Central Europe. In the current study, we identified the Nicrophorus humator Gleditsch male pheromone as methyl 4-methyloctanoate through gas chromatography/mass spectrometry analysis. In field experiments, we tested and compared the attractiveness of synthetic analogs of the male pheromones of N. humator and N. vespilloides in baited pitfall traps. An asymmetric cross-attraction to the synthetic male pheromones was observed, which is best explained by the skewed competitive relationship of the two species, with regard to the restricted availability of breeding resources. Nicrophorus humator is attracted by both its own male pheromone and by the pheromone of the smaller N. vespilloides, whereas N. vespilloides is almost exclusively attracted by its own male pheromone. The observed attraction of conspecific males of either species to male pheromone baits can be explained by both competition for females and competition for breeding resources.