Olfactory cues mediating prey-searching behaviour in interacting aphidophagous predators: are semiochemicals key factors in predator-facilitation?

Abstract

Based on their effect on prey populations, predators can interact synergistically, additively, or antagonistically. Predator attraction by semiochemicals in response to herbivory is well documented; however, the possibility of semiochemicals mediating synergistic interactions has not been explored. Eriopis connexa (Germar) and Hippodamia variegata (Goeze) (both Coleoptera: Coccinellidae) interact synergistically with carabid species in Central Chile, a phenomenon in which semiochemicals may be involved. Moreover, olfactory behaviour in these coccinellids is unknown. Olfactometries contrasting non-infested vs. infested plants with Acyrthosiphon pisum Harris (Hemiptera: Aphididae) were performed to study olfactory prey-searching in E. connexa, H. variegata, and Trirammatus striatula (Fabricius) (Coleoptera: Carabidae). To evaluate whether semiochemicals can mediate synergistic predatory interactions, four experiments were established: olfactometries contrasting (1) infested plants with and without a predator, (2) uninfested plants with and without a predator; (3) predator vs. air, and (4) plants with previous physical activity of a predator vs. clean plants (nine combinations of predator species, according to whether they corresponded to the stimulus or focal individual). Hippodamia variegata and T. striatula were attracted to infested plants when contrasted with noninfested plants. Infested plants with a conspecific and H. variegata elicited attraction in E. connexa, whereas T. striatula preferred infested plants with E. connexa or H. variegata. Treatments with only predators (with or without the plant) did not elicit responses, except in E. connexa which was repelled by conspecifics and H. variegata, perhaps indicating an antagonistic interaction between them; plants with previous physical activity of predators did not elicit responses. These results corroborated the importance of semiochemicals produced by herbivory in the prey-searching behaviour of aphidophagous predators. In addition, presence of predators on the foliage may favour emission of aphid alarm pheromones, which could attract E. connexa and T. striatula. Volatiles can intervene in synergistic interactions between carabids and coccinellids; this should be replicable in other systems where predator-facilitation between aphidophagous predators is observed.