Regulation of olfactory-based sex behaviors in the silkworm by genes in the sex-determination cascade

<p>Insect courtship and mating depend on integration of olfactory, visual, and tactile cues. Compared to other insects, <em>Bombyx mori</em>, the domesticated silkworm, has relatively simple sexual behaviors as it cannot fly. Here by using CRISPR/Cas9 and electrophysiological techniques we found that courtship and mating behaviors are regulated in male silk moths by mutating genes in the sex determination cascade belonging to two conserved pathways. Loss of <em>Bmdsx</em> gene expression significantly reduced the peripheral perception of the major pheromone component bombykol by reducing expression of the product of the <em>BmOR1</em> gene which completely blocked courtship in adult males. Interestingly, we found that mating behavior was regulated independently by another sexual differentiation gene, <em>Bmfru</em>. Loss of <em>Bmfru</em> completely blocked mating, but males displayed normal courtship behavior. Lack of <em>Bmfru</em> expression significantly reduced the perception of the minor pheromone component bombykal due to the down regulation of <em>BmOR3</em> expression; further, functional analysis revealed that loss of the product of <em>BmOR3</em> played a key role in terminating male mating behavior. Our results suggest that <em>Bmdsx</em> and <em>Bmfru</em> are at the base of the two primary pathways that regulate olfactory-based sexual behavior.</p>