Yeast volatiles show promise as a semiochemical lure for Carpophilus truncatus, an emerging pest of almond orchards around the world

Abstract

Carpophilus truncatus (Murray), a nitidulid beetle, has become a major threat to almond industries globally. While there are existing mass trapping strategies for other Carpophilus species, an effective lure for this nut-attacking pest is urgently required. This study leverages our knowledge of the chemical ecology of Carpophilus, particularly its relationship with gut-associated yeasts, to develop a new semiochemical attractant for C. truncatus. Wickerhamomyces rabaulensis was identified as the predominant gut-associated yeast in field-collected C. truncatus. Field bioassays demonstrated that traps baited with live cultures of W. rabaulensis captured more beetles compared to those baited with Hanseniaspora guilliermondii, a yeast from stone fruit-attacking Carpophilus species. GC–MS analysis revealed both qualitative and quantitative differences in the odour profiles of the two yeasts. Seven volatile compounds were identified from headspace of W. rabaulensis and confirmed to be detected by C. truncatus antennae using GC-EAD. Choice-test bioassays showed adult C. truncatus preferred a synthetic blend based on W. rabaulensis volatiles over a commercial lure designed for stone fruit Carpophilus species. Field trials with various formulations of W. rabaulensis volatiles indicated that a modified commercial lure containing isoamyl acetate and isobutyl acetate was more attractive to C. truncatus and caught fewer non-target species such as C. hemipterus. This study demonstrates the potential of insect-yeast chemical ecology in developing effective semiochemical-based lures for monitoring and mass trapping C. truncatus in almond orchards.