Marking and Deterring Oviposition on Parasitized Hosts by a Host-Marking Pheromone in an Egg Parasitoid

Mothers typically weigh reproductive options to promote increased survival and fitness for their progeny. In the important quasigregarious parasitoids Anastatus disparis, females exhibit a host discrimination ability to select fresh host eggs and reject already parasitized host eggs for oviposition. Our results from behavioral preference experiments revealed that females lost their selective preference when the parasitized host egg was extracted by the organic solvent n-hexane and preferentially rejected fresh hosts coated with the extract of parasitized hosts. These changes in selection preferences suggest that chemical cues may be used by A. disparis females to recognize parasitized hosts. In this study, which involved gas chromatography (GC) and mass spectrometry (MS), the predominant specific peak was present in the GC profile of extracts from parasitized hosts and absent in fresh host extracts that was identified as (Z)-13-docosen-1-ol. Moreover, gas chromatography-electroantennographic detector (GC-EAD) analysis revealed that female antennae responded to (Z)-13-docosen-1-ol, and the responses were (Z)-13-docosen-1-ol concentration dependent. In addition, female behavioural responses provided further evidence that females preferred to lay eggs into a fresh, untreated host when both a fresh host and a fresh host coated with 1 µl (Z)-13-docosen-1-ol (0.025 µg/µl) were simultaneously provided. Furthermore, females preferred to lay eggs into fresh hosts with lower concentrations of (Z)-13-docosen-1-ol when two fresh hosts with different concentrations of (Z)-13-docosen-1-ol were simultaneously provided. In summary, the above results suggest that (Z)-13-docosen-1-ol is likely the important active component of the host-marking pheromone in A. disparis that functions to deter oviposition of conspecifics on parasitized hosts.