Abstract
Background: Parasitic wasps (parasitoids) use volatile organic compounds released by herbivore-infested plants to locate their hosts. Response of parasitoids to plant odors may be plastic and dependent on their physiological state. Using Microplitis croceipes (Hymenoptera: Braconidae), a relatively specialized larval endoparasitoid of Heliothis virescens (Lepidoptera: Noctuidae), we asked whether age and mating status of parasitoids affect their olfactory response to host-related odors. Methods: Four odor stimuli of varying complexity were selected based on previous reports of parasitoid response to cotton volatiles: cis-3-hexenol (a green leaf volatile), α-pinene (a constitutive monoterpene), a 50/50 v/v binary mixture ( cis-3-hexenol + α-pinene), and H. virescens-infested cotton odors. Female M. croceipes used in Y-tube olfactometer bioassays were either mated or unmated, and grouped 1-3, 4-6, and 7-9 d-old. Female parasitoids used in electroantennogram (EAG) recording were mated and grouped 1-3, 4-6, 7-9 and 10-12 d-old. Results: In Y-tube olfactometer bioassays, neither age nor mating status played a major role in the attraction of parasitoids to test odor stimuli, with two exceptions: 4-6 d-old mated parasitoids showed attraction to the binary mixture, and 1-3 d-old mated parasitoids showed attraction to H. virescens-infested cotton. Age did not affect EAG response of parasitoids to test stimuli. Conclusions: The present results suggest that age and mating status do not play a major role in modulating olfactory responses of M. croceipes to host-related plant odors. Instead, plasticity of olfactory response may be limited in M. croceipes due to strong innate sensitivity to host-related odor cues.
Highlights
Parasitic wasps use volatile organic compounds (VOCs) released by herbivore-infested plants as odor cues to locate their hosts[1,2,3,4]
Effect of age and mating on attraction of parasitoids in Y-tube olfactometer Overall, there was no significant interaction between age and mating status factors for any of the four odor stimuli tested
Effect of age on EAG response of parasitoids In general, the age of mated female M. croceipes did not have a significant effect on their EAG response to test odor stimuli (Figure 2)
Summary
Parasitic wasps (parasitoids) use volatile organic compounds (VOCs) released by herbivore-infested plants as odor cues to locate their hosts[1,2,3,4]. Changes in physiological states can affect response to VOCs in parasitoids and other insects[5,6,7,8,9]. Previous studies have reported mixed results regarding age-related plasticity of response to VOCs in parasitoids, the need for further studies[14,20,21]. Using Microplitis croceipes (Hymenoptera: Braconidae), a relatively specialized larval endoparasitoid of Heliothis virescens (Lepidoptera: Noctuidae), we asked whether age and mating status of parasitoids affect their olfactory response to host-related odors. Conclusions: The present results suggest that age and mating status do not play a major role in modulating olfactory responses of M. croceipes to host-related plant odors. Plasticity of olfactory response may be limited in M. croceipes due to strong innate sensitivity to host-related odor cues
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