Olfactory responses of Theocolax elegans (Hymenoptera, Pteromalidae) females to volatile signals derived from host habitats

The responses of female Theocolax elegans (Hymenoptera: Pteromalidae) to volatile signals derived from its host habitats were investigated in a static four-chamber olfactometer. Our results demonstrated that T. elegans females, irrespective of experience, were apparently attracted by the odors released from the faeces of Sitophilus zeamais larvae and adults, which has never been investigated in previous researches. Moreover, we compared the responses of female parasitoids to odors released from grains of rice damaged by S. zeamais larvae, S. zeamais males, S. zeamais females, and mechanically. Artificially damaged grains do not emit large amounts of the volatiles that attract experienced parasitoid females to grains damaged by S. zeamais larvae. Further experiments revealed that experienced T. elegans females were more strongly attracted to rice grains which had been infused with extract from the heads and thoraxes of weevil larvae than to rice grains that had been infused only with sodium phosphate. The behavior of T. elegans females to odors released from pheromone-releasing S. zeamais males on healthy grains and unmated S. zeamais females on healthy grains were observed. The results revealed that S. zeamais aggregation pheromones are not useful signals for T. elegans females, irrespective of experience. Based on these observations, T. elegans females used faeces to detect potential hosts. Our results revealed that head and thorax of S. zeamais larvae induces rice grains to release volatiles attractive to T. elegans females, particularly after experience.