A Token Stimulus Receptor Tuned to Gluconapin in the Cabbage White Butterfly

<i>Pieris</i> butterflies recognize host Brassicaceae plants via sensing glucosinolates, but the molecular mechanism remains unclear. Here, we cloned five gustatory receptor genes highly expressed in larval mouthparts, adult foreleg tarsi, and the proboscis of <i>Pieris rapae</i> and then ectopically expressed each of them in <i>Gr5a</i> neurons of <i>Drosophila</i> and determined responses of the neurons to glucosinolates. Among them, only <i>Gr5a</i> > <i>PrapGr19</i> neurons respond to gluconapin dose-dependently. Knockdown of <i>PrapGr19</i> by 52.3% significantly reduces the firing rate of the lateral sensilla styloconica in the fifth instar larvae of <i>P. rapae</i> to gluconapin but has no effect on the responses to sinigrin and sucrose. This leads to the loss of the feeding preference of larvae for gluconapin and <i>Cleome spinosa</i>. All these results indicate PrapGr19 is the receptor mediating <i>P. rapae</i> larvae sensing gluconapin, which provides new knowledge for revealing molecular bases of glucosinolate sensing in <i>Pieris</i> butterflies.