Electroantennogram response of the parasitoid , to host - related odors : The discrepancy

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 (Hymenoptera: Braconidae). In the present study, the olfactory croceipes response of female . to synthetic versions of 15 previously M croceipes identified compounds was tested in electroantennogram (EAG) bioassays. Using as a model species, we further asked the question: does M. croceipes the relative abundance of a volatile compound match the level of antennal response in parasitoids? Female showed varying EAG responses M. croceipes 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 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, ( )-β-caryophyllene, the most abundant (29%) E 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. 1 1,2