The potential of host-specific volatiles from Tribolium confusum larval faeces for luring the ectoparasitoid Holepyris sylvanidis
The ectoparasitoid Holepyris sylvanidis (Bethylidae) attacks larvae of different stored product pest beetles. Previous studies on the olfactory host search of H. sylvanidis revealed that female parasitoids are strongly attracted to volatiles released from Tribolium confusum larval faeces, in particular to (E)-2-nonenal and 1-pentadecene. We suggested that these host-specific key compounds may serve the parasitoid as long-range attractants for host location. In this context, we propose that the attractive volatile blend could be used to establish a new approach within the biological control of stored product pests by guiding the parasitoid to its host and thus, increasing the host finding success. We investigated the potential of the identified host-indicating volatile cues to attract H. sylvanidis from a distance by offering the two key compounds to female parasitoids. Their walking behaviour and the covered distance were analysed on a Kramer sphere. Moreover, in semi-field trials both attractive volatiles were loaded onto rubber septa which were placed next to 4th instars of T. confusum at 1.5 m distance from the parasitoids. We studied the host finding success of H. sylvanidis by (i) measuring the mean time to locate and parasitise T. confusum larvae and (ii) counting the number of parasitised and unparasitised host larvae as well as the number of newly hatched parasitoids compared to the control without additional olfactory cues. First results showed that H. sylvanids females can locate the provided host larvae from a distance. Parasitistion of host larvae started four days after the release of parasitoids. No effect of the additionally offered hostspecific key volatiles ((E)-2-nonenal and 1-pentadecene) on the parasitoid´s host finding success was observed at the given conditions and used amounts of compounds. Further studies are required to determine the right odour blend and concentrations for attraction of parasitoids over a distance and finally to show that the addition of host-derived kairomones may support the host finding success of H. sylvanidis.