Evolutionarily conserved odorant-binding proteins participate in establishing tritrophic interactions

Area of Science:

• Chemical Ecology
• Insect Behavior
• Molecular Biology

Background:

• Plant volatiles mediate tritrophic interactions by attracting herbivores and their natural enemies.
• The chemosensory basis for this shared attraction, particularly involving odorant-binding proteins (OBPs), remains largely unexplored.
• The pine-attacking beetle *Monochamus alternatus* and its parasitoid *Dastarcus helophoroides* are attracted to stressed pines.

Purpose of the Study:

• To investigate the shared chemosensory basis for the attraction of *Monochamus alternatus* and *Dastarcus helophoroides* to stressed pines.
• To identify the role of odorant-binding proteins (OBPs) in the detection of specific plant volatiles by these insects.
• To elucidate the olfactory mechanisms underlying tritrophic interactions mediated by plant chemicals.

Main Methods:

• Behavioral assays were conducted to test the attraction of *M. alternatus* and *D. helophoroides* to (+)-fenchone, a volatile emitted by stressed pines.
• Two orthologous OBPs, one from each insect species, were identified and characterized.
• RNA interference (RNAi) was used to assess the function of the identified OBPs in insect attraction.

Main Results:

• (+)-Fenchone attracted both the herbivorous beetle *M. alternatus* and its parasitoid *D. helophoroides* in behavioral assays.
• The identified orthologous OBPs from both insects exhibited binding affinity for (+)-fenchone.
• RNAi-mediated knockdown of these OBPs abolished the insects' attraction to (+)-fenchone.

Conclusions:

• Evolutionarily conserved OBPs in herbivores and their natural enemies can detect the same plant volatiles.
• This conserved OBP function provides an olfactory mechanism for chemical signal-mediated tritrophic relationships.
• The findings shed light on the molecular basis of insect-plant-enemy interactions and chemical communication in ecosystems.