Candidate Pheromone Receptors of the Red-Belted Clearwing Moth Synanthedon myophaeformis Bind Pear Ester and Other Semiochemicals

The red-belted clearwing moth Synanthedon myophaeformis is a deleterious pest of apple orchards, wherein the larvae bore tree bark, resulting in reduced fitness and ultimately death. The main control strategies of this pest still rely on the use of pesticides, while alternative agronomic methods for its control coexist, with the application of the main pheromone (Z,Z)-3,13-octadecadien-1-yl acetate. Until now, the molecular bases of the chemosensory systems of the red-belted clearwing moth have been less explored. With the aim to identify novel ligands that may interfere with the behaviour of S. myophaeformis, in this study, we have isolated and functionally characterised some key odorant receptors (ORs) of this moth by selecting paralogues from two main subgroups of the Lepidopteran pheromone receptor (PR) clade: the OR3 subgroup (OR3.1 to OR3.4) and the OR22 subgroup (OR22.1 to OR22.4). We generated transgenic D. melanogaster expressing SmyoORs in ab3A neurons, which we approached by single sensillum recording (SSR). Among these ORs, we deorphanized SmyoOR3.4 to ligands that we have previously identified for orthologues of the codling moth Cydia pomonella, including the pear ester ethyl-(E,Z)-2,4-decadienoate, its methyl ester analogue methyl-(E,Z)-2,4-decadienote, and the unsaturated aldehyde (Z)-6-undecenal. With this approach, we also identified a wide pattern of activation of SmyoOR22.4 to several apple-emitted ligands. Despite the fact that combining SSR with gas chromatography (GC-SSR) did not unveil the activation of the SmyoORs to compounds present in the headspace from apples, GC-SSR unveiled the enhancement of the SmyoOR3.4 spiking at nanogram doses of both pear ester, methyl ester, and (Z)-6-undecenal. For the first time, this study deorphanized ORs from the red-belted clearwing moth and identified ligands as possible semiochemicals to add to the ongoing strategies for the control of this pest.