Reverse chemical ecology approach for sustainable palm tree protection against invasive palm weevils

Abstract

The reverse chemical ecology approach facilitates sustainable plant protection by identifying odorant receptors (ORs) tuned to odorants, especially the volatile molecules emitted from host plants that insects use for detection. A few studies have explored such an approach to develop sustainable pest management programs, especially in host-specialized insect species. We revealed the molecular mechanism of host plant detection of a destructive, invasive insect pest of palm trees (Arecaceae), the Asian palm weevil (Rhynchophorus ferrugineus), by deorphanizing an OR (RferOR2) tuned to several palm-emitted odors. We found that RferOR2 responded explicitly to several ecologically relevant palm-emitted odors and significantly to palm esters when transgenically expressed in Drosophila olfactory neurons. We mapped RferOR2 expression in the R. ferrugineus genome and found that odor specificity is likely to develop equally in both sexes. We inferred that the semiochemicals that attract palm weevils to a palm tree might aid in weevil control efforts by improving attraction, enticing many palm weevils to the traps. We demonstrate that including synthetic palm volatiles in pheromone-based mass trapping has a synergistic effect on pheromones, resulting in significantly increased weevil catches. We proved that insect OR deorphanization could aid in the identification of novel behaviorally active volatiles for inclusion in pest management. These results suggest that targeting RferOR2 may help design receptor antagonists that can interfere with weevil host-searching behavior in sustainable pest management applications. SignificanceAsian and South American palm weevils are tremendously important agricultural pests primarily adapted to palm trees and cause severe destruction, threatening sustainable palm cultivation worldwide. The host plant selection of these weevils is mainly attributed to functional specialization of odorant receptors that detect palm-derived volatiles. We unraveled the intricacies of weevil-palm tree communication by deorphanizing an odorant receptor tuned to natural palm-emitted odors. We used palm ester volatiles, which produced a significant response in the functional studies, and proved their synergistic effect on the pheromone coinciding with increased weevil catches in the field. We revealed that insect odorant receptor deorphanization could help identify novel behaviorally active volatiles (reverse chemical ecology) for sustainable palm protection.