An antennal-specific OBP mediates bait odorant perception in fire ants

Odorant binding proteins (OBPs) play a key role in the crosstalk between the external environment and dendritic neuron activation. Ham sausage is an efficient bait widely used for monitoring the invasive ant Solenopsis invicta in the field, whereas the chemoreceptors involved in bait odorant perception in S. invicta have not been functionally characterized. Here, we investigated the role of SiOBP2, an OBP specifically expressed in the antenna, from S. invicta in detecting bait odorants. SiOBP2 was specifically expressed in sensillum basiconca in S. invicta antennae and displayed strong binding affinity and diverse binding mechanisms with specific bait odorants, such as static quenching and multiple binding characteristics with 3-mercapto-2-butanone and furfuryl mercaptan. Knockdown of SiOBP2 abolished the electroantennogram and behavioral responses of S. invicta to these odorants. S. invicta with SiOBP2 knockdown exhibited inactivation of odorant receptor neuron signaling and reduced bait searching efficiency. Foraging behavior and sensory cone responses to bait odorant stimuli in S. invicta demonstrate the sensillum basiconca is particularly tuned to 3-mercapto-2-butanone and furfuryl mercaptan. Collectively, SiOBP2 is essential for the perception of S. invicta on bait odorants and can be used as an important molecular target to develop novel attractants for S. invicta.