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

Insect courtship and mating depend on integration of olfactory, visual,
and tactile cues. Compared to other insects, Bombyx mori, 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 Bmdsx gene expression
significantly reduced the peripheral perception of the major pheromone
component bombykol by reducing expression of the product of
the BmOR1 gene which completely blocked courtship in
adult males. Interestingly, we found that mating behavior was regulated
independently by another sexual differentiation gene, Bmfru. Loss
of Bmfru completely blocked mating, but males displayed
normal courtship behavior. Lack of Bmfru expression
significantly reduced the perception of the minor pheromone component
bombykal due to the down regulation of BmOR3 expression;
further, functional analysis revealed that loss of the product
of BmOR3 played a key role in terminating male mating
behavior. Our results suggest
that Bmdsx and Bmfru are at the base
of the two primary pathways that regulate olfactory-based sexual behavior.