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

Abstract

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.

Volatile Infochemicals from Rhyzopertha dominica Larvae and Larval Feces Involved in Theocolax elegans Host Habitat Location

“…Concerning T. elegans, grain volatiles were found to be perceived and attractive for both sexes [ 22 , 23 ]. The ability of T. elegans females to discriminate between infested and intact kernels has been firstly investigated by Tang [ 24 , 25 ], who highlighted that host-related substances (i.e., larval saliva and frass) can play a role in parasitoid preferences. Furthermore, experienced T. elegance females could discriminate between S. zeamais -infested rice kernels and artificially damaged ones, whereas naïve females could not [ 24 , 25 ].…”

“…Host-finding is mainly mediated by olfactory cues at long range and probably by vibrational and olfactory cues at short range [ 22 ]. Some studies aimed to investigate the role of cereal volatiles and host volatiles on the behaviour of T. elegans [ 23 , 24 , 25 ], however, it is still unclear which molecules may be involved in host selection and detection. In this study, the olfactory cues involved in the tri-trophic interaction durum wheat/ R. dominica / T. elegans were investigated in choice and no-choice experiments.…”