The semiochemical relationships in a predator-prey-host plant system were studied by a series of multiple-choice field assays. The studied system included predatory flies of the genus Medetera (Diptera: Dolichopodidae), the bark beetles Ips typographus and Pityogenes chalcographus (Coleoptera: Curculionidae: Scolytinae) as prey and Norwegian spruce (Picea abies) as the host plant. Of the nine species of predators collected, only M. setiventris and M. melancholica provided sufficient data for statistical analysis. The response of the predators to monoterpenic products of the host (alpha-pinene, limonene, camphor), pheromone compounds of I. typographus (S-cis-verbenol and 2-methyl-3-buten-2-ol) and a mixture of the pheromones of I. typographus and P. chalcographus were investigated. Our field trials revealed that tree volatiles plus pheromones of the prey, and a pheromone mixture of both prey species were considerably more attractive to M. setiventris and M. melancholica than the individual chemicals. Medetera seem to respond to the stage of tree decay and the intensity of bark beetle infestation via the ratios of tree volatiles and/or prey pheromones.
A recent study (H e t h et al. 2002) challenged the idea of “blind” foraging in herbivorous underground dwellers by showing that subterranean rodents of several species use olfaction to discriminate between soils in which plants had or had not been growing. Here we address additional questions about odour-based foraging underground. We tested responses of Zambian mole-rats (Cryptomys anselli and C. kafuensis) to putative carrot kairomones using tunnel T-mazes. Mole-rats distinguished peat moistened with hydroponic as well as filtered hydroponic “carrot water” from peat moistened with distilled water. Furthermore, mole-rats detected carrot kairomones that percolated over the course of a week through the soil to a distance of 30 cm. These results demonstrate that 1) Attractiveness of soil is given by contents of primary root kairomones not caused by microbial activity in planted soil. 2) Carrot-kairomones are water-soluble molecules of less than 0.6 μm diameter. 3) Carrot-kairomones diffuse around the plant, making plants detectable from a distance.