Caterpillar footprints as host location kairomones for Cotesia marginiventris: persistence and chemical nature.
Herbivores walking over the epicuticular wax layer of a plant may leave tracks that disclose their presence to hunting predators or parasitoids. The braconid wasp Cotesia marginiventris is a solitary parasitoid of young noctuid caterpillars. It can locate potential hosts from a distance by orienting toward the scent of herbivore-damaged plants. Upon landing on the caterpillars' food plant, the female parasitoid searches for further cues (kairomones) that confirm the presence of a suitable host. In a previous study, we showed that C. marginiventris recognizes the chemical footprints of absent Spodoptera frugiperda caterpillars on a leaf. Here, we report on the persistence and chemical nature of this host location kairomone. In a series of behavioral assays, we confirmed that caterpillars of S. frugiperda leave chemical tracks that elicit characteristic antennation behavior in C. marginiventris for up to 2 days. Both hexane extracts of caterpillar footprints and of the larvae's ventral cuticle induced antennation and contained almost identical long-chain hydrocarbons, thus suggesting the prolegs and claspers as the kairomones' main source. A series of linear C(21) to C(32) alkanes accounted for ca 90% of all identified compounds. Female wasps showed significant antennation responses on leaves treated with a reconstructed blend of these n-alkanes. However, wasp responses were relatively weak. Therefore, we presume that minor compounds, such as monomethyl-branched alkanes, which were also found, may contribute additionally to host recognition.
Rostás
Michael
M
Department of Botany II, University of Würzburg, Germany. michael.rostas@botanik.uni-wuerzburg.de
Wölfling
Mirko
M
D000475:Alkenes / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D005247:Feeding Behavior; D005260:Female; D006790:Host-Parasite Interactions; D010675:Pheromones / Q000737:chemistry* / Q000378:metabolism*; D018515:Plant Leaves / Q000469:parasitology; D018411:Spodoptera / Q000737:chemistry / Q000469:parasitology*; D013997:Time Factors; D014863:Wasps / Q000502:physiology*
D000475:Alkenes; D010675:Pheromones