Yes, it's our old friends the honey bees. They can't resist this invasive plant which has taken over many areas.
Japanese knotweed is here to stay. In my opinion the flowers are pretty, but I don't want it in the garden. There's enough out there growing wild as it is.
The bees can turn what they get off the flowers into an amazing fall honey, the color of coffee. So it does have some redeeming quality.
The only way I know to get rid of it is continual top cutting. I got rid of a patch by weed whacking the tops down to the ground every week for two seasons.
The plant sends energy to the roots through its top growth. By removing the stems and leaves, eventually the roots are starved and can't persist.
Either you will exhaust the plant or it will exhaust you!
It's quite an irony that an invasive plant which is the scourge of many gardeners provides such an amazing resource.
Nature is amazing.