Entomopathogen-associated volatiles enable parasitoid host discrimination via selective odorant receptor activation

Parasitoid wasps and entomopathogens are often jointly employed in biological control practices.For parasitic wasps, choosing a suitable host is the key to ensure optimal survival for themselves and their offspring, and consequently for their effectiveness in biological control.However, the mechanisms of how parasitoids choose between healthy hosts and those infected with entomopathogenic fungi are still elusive.Here, we found that Scleroderma guani, an ectoparasitic wasp preferentially choose a healthy host, Monochamus alternatus, rather than hosts infected 4 days after by Beauveria bassiana.The volatile methyl cinnamate emitted from B. bassiana was found to play a key role in this host selection process.The corresponding odorant receptor SguaOR48 was identified from the genome of S. guani and visualized its co-expression with SguaORco in antennal sensillae.Furthermore, by knockdown SguaOR48 expression in vivo, we demonstrated that the repellent response of S. guani to methyl cinnamate was abolished.These findings suggest that S. guani can determine the status of a host based on odour and avoid parasitizing unfavourable hosts.Our study sheds valuable insights into the molecular mechanisms behind host selection and trade-offs by parasitic wasps, and may also provide an opportunity for synergistic and efficient use of dual biocontrol for pest management in general.