Thanks, DeEtte, 

This is not an issue I knew anything about. In my research to answer your question I learned that the chemicals produced by Nandina domestica are from a class called the cyanogenic glycosides. As the name suggests, when some birds eat the fruit of this plant they experience cyanide poisoning. One study pointed out that the the cyanogenic glycoside levels are highest when the fruits become ripe, but then decrease in the months after. I could find no reports of these compounds in the nectar, but cyanogenic glycoside (likely not the specific ones found in Nandina domestica) are found in the nectar of almonds and are readily ingested by honey bees with no ill-effects. 

Best,
Andony