Electroantennogram responses of a parasitic wasp, microplitis croceipes, to host-related volatile and anthropogenic compounds

The parasitic wasp Microplitis croceipes (Cresson) (Hymenoptera: Braconidae) showed its own characteristic electroantennogram (EAG) response profiles to 13 host-related (cis-3-hexenol, α-pinene (R)-(+)-limonene (S)-(-)-limonene, trans-β-ocimene (±)-linalool, (-)-trans-caryophyllene, α-humulene, nerolidol, trans-nerolidol, cis-nerolidol, methyl jasmonate and indole) and four anthropogenic (2-diisopropylaminoethanol, 2,2′-thiodiethanol, 2-methyl-5-nitroaniline and cyclohexanone) volatile compounds. These profiles were similar between males and females except for 2-diisopropylaminoethanol, which elicited significantly larger EAG responses in males. Among the compounds tested, cis-3-hexenol, linalool and cyclohexanone elicited the largest EAG responses. EAG responses were not influenced by the age of wasps between 1 and 13 days after emergence. EAG responses were dose-dependent, and highly EAG-active compounds elicited significant EAG responses with less than 10 μg of the compounds at source. Quantification of compounds released from an odour cartridge indicates that release rate is highly dependent on the chemical nature of stimuli, showing up to 10 000-fold differences in the amount released between different compounds when the same amount was loaded in the odour cartridge. Wasps having undergone a behavioural training regime to be attracted to either cyclohexanone or methyl jasmonate did not show any differences in EAG responses from those of untrained wasps.