Electroantennogram response of the parasitoid, Microplitis croceipes to host-related odors: The discrepancy between relative abundance and level of antennal responses to volatile compound

Abstract

Herbivores emit volatile organic compounds (VOCs) after feeding on plants. Parasitoids exploit these VOCs as odor cues to locate their hosts. In nature, host-related odors are emitted as blends of various compounds occurring in different proportions, and minor blend components can sometimes have profound effects on parasitoid responses. In a previous related study, we identified and quantified VOCs emitted by cotton plant-fed Heliothis virescens (Lepidoptera: Noctuidae) larvae, an herbivore host of the parasitoid Microplitis croceipes (Hymenoptera: Braconidae). In the present study, the olfactory response of female M. croceipes to synthetic versions of 15 previously identified compounds was tested in electroantennogram (EAG) bioassays. Using M. croceipes as a model species, we further asked the question: does the relative abundance of a volatile compound match the level of antennal response in parasitoids? Female M. croceipes showed varying EAG responses to test compounds, indicating different levels of bioactivity in the insect antenna. Eight compounds, including decanal, 1-octen-3-ol, 3-octanone, 2-ethylhexanol, tridecane, tetradecane, α-farnesene and bisabolene, elicited EAG responses above or equal to the 50 th percentile rank of all responses. Interestingly, decanal, which represented only 1% of the total amount of odors emitted by cotton-fed hosts, elicited the highest (0.82 mV) EAG response in parasitoids. On the other hand, ( E)-β-caryophyllene, the most abundant (29%) blend component, elicited a relatively low (0.17 mV) EAG response. The results suggest that EAG response to host-related volatiles in parasitoids is probably more influenced by the ecological relevance or functional role of the compound in the blend, rather than its relative abundance.

Molecular Characterization of Three Chemosensory Proteins from Carposina sasakii

“…Interestingly, Morawo et al found that decanal elicited 0.82 mV EAG response in Microplitis croceipes, which was the highest response value. However, decanal accounts for only 1% of cotton-fed host volatiles [69].…”

Deorphanization of an odorant receptor revealed new bioactive components for green mirid bug Apolygus lucorum (Hemiptera: Miridae)

“…For comparisons between means, analysis of variance (ANOVA) was conducted, followed by the Tukey's HSD (honestly significant difference) test (significance level: P < 0.05). In EAG assay, data were calculated as absolute values by deducting the control (solvent) responses from treatment (component) responses . Student's t ‐test ( P < 0.05) was used to determine the differences in EAG values between males and females.…”

“…In EAG assay, data were calculated as absolute values by deducting the control (solvent) responses from treatment (component) responses. 32 Student's t-test (P < 0.05) was used to determine the differences in EAG values between males and females.…”

Insect olfactory system inspired biosensors for odorant detection

“…The signals can be assessed and analyzed with other software. 47 With the help of advanced data acquisition analysis systems, electroantennograms have been successfully employed to establish olfactory biosensors for a wide variety of odorant identifications. [35][36][37] For instance, using the antenna of the Colorado potato beetle, an electroantennographic detector was successfully used to detect volatile organic compounds emitted by its host plants, which could also be used to explore the plant-insect interactions.…”